[@lugubrious] I agree with [@zarkun] about the fact that it works quite well for this system. Yes there are bad pokemon, but that's true for all evolution lines, not just the non-evolving lines. I think the main reason the non-evolving pokemon are in that category's 'cuz they're technically fully-grown by that form, and if you make some assumptions about the whole "strong wills" concept it makes sense.