I don't remember an AC bonus by level in 3e, except as a variant in a supplement. In 4e, the sum of reciprocal chances to hit seems to stay about the same, so a bonus for me is a penalty for you.
My impression is that the Powers system has a similar effect, more pronounced than Feats in 3e.
Above all, the recovery of resources between "encounters" means that attrition is not the factor it used to be.
I'm not a 3e maven, but in AD&D a 13th-level fighter might have twice the chance to score a hit vs. plate as a 5th-level one -- but get worn down to half the hit points (or less). Heck, it's possible (if improbable) that the Lord would start with less at peak. (e.g., poor avg. 3 x 13 = 39, vs. good avg. 8 x 5 = 40)
If memory serves, h.p. recovery in 3e -- both innate and magical, the latter depending on caster level -- got a level bonus. However, both resources were still basically on the old daily time scale.
... whereas in old D&D, x.p. and levels both are artificial constraints only on the particularly fantastic elements that figure in the "dungeon adventure" scheme.
If something does not earn x.p., then neither does it require them! My fighter can also be a lover, a scholar, a gentleman, a philanthropist and an intriguer regardless. He can go on to more such accomplishments even if he happens also to have hit the level limit for a Hobbit.
D&D is other games built upon different ideals.
That is one big problem here.