There is little or no case to be made for Mollema being a stronger climber, certainly not one stemming from the Vuelta. Better GT GC rider yes, better climber certainly not. Martin attacked on pretty much every mountain stage at the Vuelta, sometimes attacking on the penultimate climb as well as the final one, won a MTF, and still beat Mollema up to the top as often as Mollema beat him sitting with the favourites. If you are as good or better while riding in a considerably less optimal manner (because you want the win not time), you are stronger. At full gas on a good day for each, Martin is a stronger climber.
Mollema's advantage over Martin came from the Time Trial and to a lesser extent from one single bad day. That bad day represents his advantage in consistency, which is actually less than I'd have put it at before the Vuelta. Martin was surprisingly consistent for a rider with a reputation for challenging for a win one day and being in the autobus the next. He had one bad day and even that wasn't a disaster. However, he was dire in the Time Trial and unless he improves drastically at that, will never be as good a GC rider because a marginal advantage as a climber doesn't compensate for the stupid sort of time he gave away against the clock.
If Martin can improve his time trial, the Vuelta convinced me he can be a GC rider. But that's a big if. If I was part of Garmin management, I'd have him spend the entire period between the end of Catalonia and the end of the Giro, when his allergies screw up his competitiveness going around and around some indoor track on a time trial bike. With David Millar hitting him with a stick every time he gets out of optimal position. He'll never be a very good time triallist because his build is all wrong, but there's absolutely no reason why he can't learn proper technique.