One thing you have not considered is that when a certain skill/spell is attained, it makes killing significantly easier. So if you try to spread the xp load around more evenly, it does NOT necessarily make levelling even. In fact, it may make it much longer to level at the lower levels than at the higher levels.
Also bear in mind, even if you do not gain any new skills or spells, your attack, defence, etc do go up. Changing tiers makes a significant difference as well, gaining a huge speed boost.
Other than that, we already know the system is horribly unbalanced anyways.