Leagues ahead? No way. Is he better right now overall? Yeah. But if you're asking me who I'd want for a big game I'd take Harden. Both are improving young players, but if Westbrook doesnt make huge strides in the next 2-3 years in his decision making in the halfcourt vs good defences, I'll take Harden because his decision making is awesome and his game is improving a ton year to year as well.
This question is all dependant on Westbrooks maturity going forward. He's obviously a super talented PG who is capable of being a top 3 PG, but if he'll ever get there is a whole other question. He only holds himself back.