Why can't we have both?
Reaaalllllyy slow exp gain for playing normally (like just add a huge-ass x.05 multiplier on normal exp earned from matches so 20 matches turns into 1000 matches) and give Achivements high amounts of exp in addition to their current rewards.
That way, if you really, really, REALLY care about this game, but can't get achiveos because you have no skills, you have a slow way of crawiling up top, and at the same time, promotes actually earning skills for achiveos to get your levels.