Wulf Ratbane said:
I think 3e's problems in this regard are closer to this:
1) Too many ways to accumulate bonuses make the gap appear faster (ie, bonus stacking issues)
2) Players have way too much control over their ability to accumulate those bonuses.
I'd fix one, if not both, of those things, before I'd move to a 1/2 level +X flat scale for all classes.
Absolutely right, and it seems that 4e is trying to prevent those things, too. But the problem with the 3e progression is that you end up with inevitable large gaps. At 20th level, the gap between the best and worst BAB is +10, and between good and bad saves is +6. On top of that, you're generally better off improving your strengths (through ability scores, feats, and magic items), so the actual gaps become much larger. It's built into the system.
So a wizard, for example, sucks at anything that requires an attack roll, at least vs. normal AC. She needs ways around it, which she gets with spells that target touch AC (which can be absurdly low), Fortitude or Will saves (which can also be absurdly low), or massive-damage area attacks that still do damage even on a failed save (barring evasion). The smart wizard can choose her targets appropriately, making the effects much more devastating, due to the variation between good and bad defenses. Thus, we find ourselves at the point where the fighter feels incompetent in combat, serving only as a front-line damage sponge while the wizard cleans up the opponents. While not everyone feels that way about higher-level melee combatants, many do, and it's a big issue for them (and the reason that
Bo9S was so well-received).
In the 3e sweet spot, characters have enough choice in their attacks and enough staying power to make things interesting, and the variations in good/bad attacks/defenses per character and between characters are broad enough to make a meaningful difference, but not so broad that they inevitably make anyone feel useless in some important aspect of combat. The idea behind the +1/2 per level in 4e (as I understand it, not having seen the system yet) is to keep everyone on the same scale, while allowing the scale to increase so that you get the traditional D&D feel of ever-increasing power and skill. The variation will come in the form of (a relatively small number of) bonuses due to class, weapon, magic, feats, etc., and more choices on everyone's part to direct attacks against different defenses.
I share part of your feeling that the +1/2 bonus per level might have the effect of mushing everyone into feeling too similar. I'm hopeful that there are enough meaningful bonuses that it won't be an issue in play, while not so many that they run away with the game.
