1. Some feats are OP, Sharpshooter and Great Weapon Fighter would be on this list, I would probably add healer feat these days.
They’re a bit above the curve, but I wouldn’t call them overpowered. All of the highest damage builds make use of them, but unless you’ve got a group of hardcore character optimizers, they’re not even a problem most of the time. And even if you do have such a group, they don’t break the game.
2. Feats in general break the game (in the PCs favour). Big offenders here are warcaster, resilient: con, and healer as they tens to negate the concentration mechanic and pacing of the gamer.
Nah, Feats are generally fine. These ones aren’t problems at all, because Concentration is its own limiting factor. Sure, you can keep up concentration on one spell despite being hit, but that’s not really a problem because you can only Concentrate on one spell at a time, and the spells are balanced with the expectation that you can maintain them for their full Duration if you want to.
3. Dex is stupidly OP unless feats are used (assuming you are melee, there is still sharpshooter).
Dexterity is still pretty much the god stat, yeah. I wouldn’t describe it as “stupidly OP”, but it is probably better than it should be.
Nah. Bless is really good at helping you succeed at rolls, which is working exactly as intended. If your game is broken by players consistently succeeding at rolls, you have bigger problems than Bless.
5. The encounter guidelines did not work that well past level 10 or so (or 7 perhaps).
Yeah, but what else is new. 4e was the only Edition whose encounter building guidelines didn’t suck.
6. High level 5E was stupidly easy even ignoring the encounter guidelines with combats X5 deadly.
You get to a point after a while where the party’s victory in any fair fight is more or less assured. I’m not sure if this is a feature or a bug. At any rate, it is entirely possible to challenge a high level party, but it might require a little creativity. Legendary Monsters are generally a good place to start.
We did inadvertently stumble on some of the most powerful archetypes early on- light/life cleric, lore bard, diviner, paladins, battlemaster fighter but we also had war clerics, hunter rangers, rogues, champion fighters. We had magic weapons of course but early on most of them were from LMoP although I made the mistake of placing a +2 hand crossbow.
Life Cleric is one of the few things in the game I would describe as OP. Lore Bards can break the DC math, but again, if the PCs consistently succeeding at checks breaks your game you’ve got bigger problems. I haven’t found the other builds you mentioned to be OP at all. +X magic items do break the difficulty curve, but that’s working as intended. If you give the PCs +X magic items, you should expect them to be able to handle higher CR fights.
Now on ENworld and other sites the same complaints tend to come up again and again. So here we are 3 years later, was I right, wrong somewhere in the middle?
Somewhere in the middle. You correctly identified the most powerful options and builds in the game. You just have a different standard of OP than I think most folks do.