Hmm, I don't think it's actually that different between 3.5e and 5e once you're high level. AC is universally lower in 5e compared to 3.5e. Recall also, in 3.5e your subsequent attacks each take a -5 penalty (i.e. a lvl 20 Fighter BAB is 20/15/10/5)
A 3.5e lvl 20 fighter with +(35/30/25/20) AB vs. 39 AC = hit chance of 85% / 60%/ 35% / 10%
A 5e lvl 20 fighter with +14 AB (x4) attack vs 22 AC (Ancient Red Dragon) = 65% / 65% / 65% / 65%
Epic level is not lv 20. Is
above lv 20. 3.5e and 2e din't followed the "tiers" that 5e sadly brought from 4e. An lv 1 mage is a guy who casted the first spell today, a lv 20 is the guy who mastered the arcane arts and above lv 20, he broke all human limitations.
I used level 20 in both cases because 5E doesn't have epic level rules (yet). And it makes far more sense to compare same level to level.
Despite the
naming of the tiers, the 3.5e and 5e characters still advanced in the same way. You still get level 9 spells at level 17, and the Monster CR are roughly equivalent in both editions (i.e. strongest Dragons are all around mid-20s CR).
3.5E's epic rules were 100% supplementary - not part of the Player's Handbook (which also went up to 20). It was also terribly balanced - as epic martials without insane min/max-ing via prestige classes from in supplementary material are a joke (they'll soundly lose to pre-epic casters). Nevermind that AC scaled so better than AB in 3.5 that martials will eventually not be able to even touch themselves. BTW, in 3.5e, epic fighters and wizards had the same attack bonus scaling (1/2) in epic levels.
Also, you are ignoring that attributes, feats and gear has a HUGE IMPACT on Attack Bonus.
A epic level warrior would probably have a +5 weapon. Magical items and weapon focus, greater weapon focus, epic weapon focus and weapon specialization.
I used pretty typical numbers for both editions (not super-munchkin, but respectable).
35 AB = +20 BAB, +5 Weapon, +8 STR (26*), +2 Feats (Weapon Focus, Greater Weapon Focus)
*16 Starting + 4 Levels + 6 Giant Strength Belt. You have to remember Pathfinder/Kingmaker and its +8 every attribute items are an oddity when it comes to table top games. Items in the 3.5 DMG mostly only went up to +6. BTW, the specialization feats only add damage, not Attack Bonus.
The same applies to spell resistance on 3.5e. Most casters would have spell penetration and greater spell penetration and some enemies on kingmaker like spawn of rovagug are hard to hit even at lv 20 with both feats. He has 42 SR if I remember correctly.
He is a hard enemy due regen, resistances, immunities, summons, powers, damage dealing, etc; not only due a hp bloat...
I thought your point was that things in 3.5 were easier to hit and less dependant on RNG? Granted, Pathfinder is not 3.5e - it's a bit more higher power, and Kingmaker is even more so.
A 42 SR would mean a level 20 wizard with both Spell Penetration feats (+24 total) has a 15% chance of landing a spell that checks for SR. IIRC his SR in core difficulty is in the mid-30s, but that's still high enough to make magic use against him basically RNG.
It's funny that you bring it up because the Spawn of Rovagug in Kingmaker is EXACTLY the thing you're complaining about. HP Bloat (1.5k HP), and high Spell Resistance = making spell attacks useless.
Guess what? It works just fine in Kingmaker, because the game
doesn't follow PnP, and is designed in a way that you get insanely good equipment. 1500 HP and 40 HP regen isn't that much when your characters in Kingmaker can put out 600+ damage per round, and trivialize his AC and DR with Smite, etc.