4E epic levels were on paper only. They basically stretched level 3-10 over 30 levels and bloated the HP.
Pull out a 4E phb and look at the level 29 powers. They're about on par with 5th level spells in 5E and 3.5. That's level 9 and 10. Cantrips scaling at level 21 is another example.
Eh. The levels are stretched but you actually get to do Epic things in the Epic tier, including planar travel, self-resurrecting, and fighting gods which make Auril in Rime of the Frostmaiden look paltry. The first full campaign I played in was a level 1-30 which climaxed with defeating Orcus and then Vecna, my Epic Trickster Rogue striking him down wielding The Sword of Kas in The Hand of Vecna.
"On par" with 5th level spells? Not exactly. Although there are a few legacy spells in D&D which are massively powerful at 5th or 6th level because those were the original top level spells in 1974. Reincarnation, Commune, Raise Dead, Death Spell, Geas, Disintegrate, Control Weather. Gary already jumped the shark in 1975 adding 6th & 7th for Cleric and 7th-9th level spells for M-Us, most of which (except Wish) really are on par with the original top-level spells.
Which powers or spells from other editions' Epic levels strike you as both playable and more epic?
4E MM another example. Bloated HP very low damage.
Worse you already know how the combats going ro end. You just have to spend 45 minutes-2 hours to get there. No tension pre determined results. Ultimately it's boring.
The first 4E MM had some flaws in the stats, as everyone knows. Though the powers, thematic roles, and tactical play still kept most of the monsters fun, as opposed to the perennial "bag of hit points" complaint about 5E. Most 4E monsters are fun and interesting and present tactical challenges even in the absence of interesting terrain. Most 5E monsters are inherently boring unless you add interesting terrain and objectives other than whittling down the HP.
Whether fights are boring because you know you're going to win most of them...? Kind of a matter of taste. That's always been true of D&D, because as soon as a fight gets scaled close to 50/50 odds, the PCs are almost guaranteed to die after only a few.
50% of surviving any given fight = 25% of surviving two = 12.5% chance of surviving three = 6.25% chance of surviving four fights.
While mathematically the lower hit points relative to damage of the TSR editions meant they were more lethal and scary, in practice DMs fudged and/or players stacked the deck with Sleep and cheap plate mail so as to make their odds of winning much higher than 50%.
"Bloated HP" do have the virtue of giving more opportunity to make decisions about whether to run or try a different tactic. If you're a low level TSR edition Fighter you're almost always 1-2 hits from death, which isn't a lot of decision space. Of course, once you hit 4th or so you now have reliable padding of HP for a couple of fights, and if you have healing magic handy you're MOSTLY out of range of a one hit kill (with poison and such being scary exceptions; albeit ones people complained about).
I will agree that an issue is fights taking too long. Whether that's because either or both sides just have too many HP, or because of a lack of morale or similar rules to cut them shorter once the ending is clearly determined.
AD&D you might make a save 95% of the time but you can always roll a 1 and die. The odd of a TPK needs to be there and the odds of that happening are fairly low comparatively. Shadow Dragon in 2E eep. Death has very real consequences as resurrection isn't guaranteed and your con score drops.
Yes, those 5% chancers were always exceptions, but could crop up. Level drainers and con drainers in the TSR editions were famously scary but also widely hated. Ability damage was a notorious killer in 3.x, but of course more the exception than the rule.
Even in AD&D death was the exception rather than the rule, or people would never gain levels.
Basically every edition, 1974-2008, made PCs progressively tougher.
Runable and fun? Yes.
But too time consuming. Emphasized by the fact that adventures had too many encounters.
Of we were young and played a whole day every week, we could have appreciated it. When you only manage to play a few hours per month, manageable and fun is if the combat is just done in less than half an hour.
Worked fine for regular weekly 4-ish hour sessions, IME. I get that a lot of people are gaming less than that nowadays, of course.
4E did have some flaws. Off-turn actions and certain classes dependent on reminding other people of stuff every turn (Shaman was ROUGH) could really slow stuff down. Players who get analysis paralysis and can't make up their minds what to do among their powers were (and always have been, and likely always will be) a problem, but the Essentials classes at least gave them some simpler options. When it was humming, individual turns were quick, but you got more of them.