I'm not going to argue with you that the ruleset doesn't work for your group at high level but I have to comment on a few of these. This is purely combat that you're speaking about so I'll just speak to combat. I don't know how many players you have in your group. I have 3 and we've run through epic tier twice now. I have my concerns about large groups at epic tier due to (i) sheer table handling time per round as numbers creep up beyond "standard assumptions" (4-5 PCs) and (ii) the impact of synergy (specifically vulernability synergy and action denial) once you move into 7 + PCs.
Actually, for my group and I, the math and design no longer works at Epic levels. The characters are too powerful, have too much personal "turn time" with action points, extra actions, and number of attacks, etc. Individual players' turns can take 5 to 20 minutes.
5-20 minutes? Per turn? Is this meant to be per round?...with a group of 8 + players? This is ghastly and is so beyond the pale of my experience that I can't even fathom it. Its akin to introducing a fish to a bicycle. My players are all optimizers (each with a varying suite of minor, move, free, no, immediate actions) yet all are efficient and decisive in their tactical decision-making. The have multiple dice for AoEs, go clockwise in their attack rolls and quickly perform their (simple) math. No turn...ever...not...once has taken anywhere even close to 5 minutes. Not ever. At Epic tier, their typical turn in a boss fight is somewhere in the area of 1 minute, shooting up to the extremely rare 2 minutes when they are deploying action points, minors et al, and resolving significant AoEs. This includes fortune in the middle fictional narration and retrofitting as required. L + 2 fights? Standard turn is probably 45 seconds and doesn't deviate much from that. 5-20 minutes? Per turn? On average? I cannot even come up with a scenario at the table where this turns out. I don't blame you for hating the ruleset. If one of my players took 20 minutes on their turn, I wouldn't be posting this because I would be in the federal penitentiary serving 20 to life.
I've come to despise the codified minor/move/standard/opportunity/immediate reaction/immediate interrupt action economy. People feel they need to milk as many actions and fiddly bits as they can, and they rarely remember to do so. How many times have we moved to the next turn or even round, just to have someone remind themselves or someone else that they "forgot that ability" or "should have done this", or "meant to do this, too"? I cannot tell players not to play on their iPads or smart phones, or read a book, or talk about other things, because they won't get to act again for another 30 to 40 minutes.
Again, this is so far outside of my experience that I cannot even fathom. I'm sure its happened to you though and I sympathize because if this was standard fair at my table...20 to life in the federal penitentiary. I have no idea how you are still a free man. You must have the patience of 10 saints.
For instance, the dismissal/vulnerabity/alpha strike tactic makes it so that fights (including MM3+ solos) can barely function unless they are many levels higher than the party. Tactic: Cast Dismissal on the nasty solo (which is at least an auto-dismissal for one round). Everyone ready for the Cleric to give the bad guy Vulnerability 15 when the bad guy returns. Then everyone hits the bad guy with every last multi-attack they can muster. Result: Deal 400 to 600 damage in one round.
As far as this goes, its an extreme corner case. All new Solos have action denial protection in the way of automatic stun, daze, dominate, etc removal either at the end of their current turn or on their next intra-round Init-10 suite of actions. In this extreme scenario, I presume you're talking about:
1 - 10 player group setup as a Radiant Mafia (everyone has a radiant attacks); If somehow, every single one of those 10 players manages to successfully land 3 - 4 attacks (perhaps 4 attacks at 75 % hit rate or 5 at 80 % hit rate), that would be 450 - 600 damage nova from the radiant vulnerability 15. There are few classes that have at their disposal a 4-5 attack nova (even in AP round). I don't know of a single one of those classes that can do it as Radiant damage; not Avenger, Paladin, Invoker, nor Cleric. The Cleric below in 3 can use a Daily Utility to give one single character a weapon that does Radiant attacks. The only ability I can find that provides an aura or zone that allows every ally to attack with the Radiant Keyword is the Sainted General Paragon Path Level 12 Daily Heaven's Warriors....and that is a Standard Action. I'm assuming there must be a Sainted General in this group that spends his Readied, Standard Action to use this ability...thus cutting the group to 9...making the landed attack requirement/character even greater.
2 - and a Cleric who has (presumably precisely for this nova setup) kept Dismissal (Level 9 Daily Prayer) in the stead of an upgrade at 19 (which in pretty much every circumstance will be a better power).
3 - who worships Selune (or a God(dess) of the Moon, etc) and has access to the Channel Divinity Life and Light as it is the only Vulnerable 15 Radiant available to Clerics and costs a Standard Action.
Again, Vulnerability cheese as force-multiplier is a known problem in 4e...that is undeniable. And Radiant Mafias are the worst offenders (made worse the larger the group). However, this setup would be more deadly and more ridiculous if the Cleric just eschewed the whole Dismissal route (which requires a successful attack for it to work) and just went Morninglord Paragon Path and inflict Vuln 10 Radiant on each successful hit. All of that being said, what you have here is an extraordinary outlier of a group setup.
And truly, this isn't even the worst of what you can do in 4e if you really just want to pervert things. You can make unhittable characters that can run 200 mph and wipe the floor with every solo in one round if you're willing to munchkinize your game and turn it into a freak show...but what exactly is the point? That says nothing about standard fair, 4-5 player groups who work off of normal assumptions and optimize under those normal assumptions. Again, my 3 players are all optimizers and we often use a metagamed Warlord (representing luck, manifest destiny and extraordinary group coordination) as a "4th character" force multiplier and nothing like what you have depicted above manifests.
The game is is still broken at Epic and I honestly don't know if I'll ever want to run Epic again. I've been running Epic games for years because players want their characters to "finish". But no previous edition of the D&D game has ever gotten it right, mechanically.
From a thematic-content perspective, it is as problematic as ever to properly deliver, I agree. There is tension in that we all seem to want to keep the mundane, familiar quality of the game but by its very nature the game turns into a superheros romp due to the potency of the players (on both sides of the conflicts) and the inevitable world (or cosmological) affecting stakes.
And do you know why my players still love my game and have fun? Because I don't tell them how much I have to break or ignore the system in order to make it fun and challenging. I love the stat blocks for monsters because they are sooo wonderfully templated. But that does not make encounter creation a snap. That is a fallacy. The math and design conceits around encounters and the game as a whole make the game not work and untenable in my experience.
Again, I don't know your group setup but you have my sympathies. I run Level + 2 as standard combats and L + 4 or 5 as boss level combats with hazards, terrain powers and all manner of mobility/forced movement and my encounters work with nearly flawless predictive power (for me), exciting dynamism and never fail to produce the genre relevant climax we're looking for. I've never had to even think about (nor would I) using GM force to circumvent legitimate mechanical resolution of conflict to make the game "work."
Not only that, but because the power cards are very specific and encourage the feel that they "must be used or you are not pulling your weight," our game rarely sees players acting upon inspiration, or innovating actions decsions that are not connected to power cards. The fights are power-spam slogs. It's like Final Tantasy Tactics. We role-play outside of combat, but when a combat occurs, the role-play stops and we create a battlefield, and play a board game.
Again...no resemblance to my table. Pretty much every battle is different from the last. Combat lasts perhaps 4-5 rounds and maybe 7-8 for boss fights. There is probably 2-3 uses of p42 in our 4-5 round fights and the boss fights are absolutely rife with them due to the setup of hazards and terrain powers; probably 2 per player in those 7-8 rounds so perhaps 6 total on average.
I am soooo looking forward to a breath of fresh air. And as much as I enjoyed each edition of D&D because I love the story, and I love playing with my friends, I really want the old flavor coupled with the innovative reimagining and redesign I've been seeing in D&D Next. This is exactly what I am hoping for. They are designing in the right direction for me. And I will provide feedback to the very end to help it become the best it can be.
In my opinion...
I can understand this given what you have described. I would have abandoned 4e long ago...primarily because I would likely have been serving life in prison for a bloody massacre of my players for a 10 player group, Radiant Mafia cheesing, 5-20 minute turn taking (yet somehow spending all of that time never improvising and just pressing encounter001 attack buttan), Final Fantasy Tactics boardgame (as you put it) monstrosity.
5e plays like an elegant, Moldvay Basic-esque evolution of 2e with 3.x PC build schemes. The action economy and tactical depth is toned down considerably from 4e, but there are still immediate actions with a reasonable capacity for all Classes/builds to make use of the supplementary action economy so beware of that (as you indicated disdain for it in 4e). I've playtested it aplenty and you won't be seeing your 5-20 minute turns, of that I can assure you. I suspect, given your description of your 4e game and your displeasure, 5e should indeed be a breath of fresh air for you.