Even if the abilities are based on percentages, it still doesn't mean they're going to be balanced on each character level, and as such I'm pretty sure the developers have tried to balance them to level 60 rather than the lowest levels. Also, at level 13 your gear is going to be shit, so all your percentages are going to be off (lifesteal, crit, and so on). You won't have a decent companion, and so on.
Seriously, I've been reading up on the abilities ever since the first ability was made public. That's just pointless theorycrafting with no maxlevel basis. You can base your feeling about the balance of the characters on level 13 experience if you like but it won't mean much at level 60. That's just a simple fact.