Lennert much more consistent. Not sure about three weeks, but he'll definitely be a player in your average Paris - Nice.
I wouldn't say more consistent, he's just way lighter and climbs way better. Wellens is probably a better rouleur and also better for flemish races (I never understood why he focussed on the Ardennes for so long).
If he ever will be a GT rider is obviously too early to tell, but after De Lie he's a 2nd gift from God for Lotto.