Using XP progression as a balancing tool would be fine if there had ever been any effort to balance along the XP axis. Unfortunately, the use for the progression charts was simply to enforce growth that appeared simulationist. Thieving is easy, wizardry is hard, so wizards will require twice as much XP per level! Druids become hierophants after level 15, so they'll require 500,000 XP a level now!
I'm fine with different XP progression, I'm fine with levels that mean different things to different classes. But there should be some scale built into the game of measurable capability. Whether that be XP or level or something else, there should be some numerical value on the character sheet that indicates to the DM what sort of challenge the character can face.
Ultimately, level is a function of XP and class. (Level = f(class,XP)). XP is a function of player skill, time invested, and DM campaign settings. To my mind, the goal should be that players of equal skill should be rewarded with equally powerful characters.
With that goal in mind, classes should either be balanced at all XP values to ensure that the more skillful players gain levels faster; or that imbalanced classes grant levels at different XP plateaus, because it takes less skill to gain XP in an encounter with a more powerful class. (Ergo, weak classes need the least XP, since they required the most "expenditure" of skill to reach that point).
If you don't believe in rewarding player skill, but rather participation, then the 3e-4e progression makes the most sense. It gives you the best scale for measuring baseline capability, as well as granting equivalent rewards to the players.