Yes, to be fair to Marcelo he has improved in attack and also a little in defence, but he's never really tested in La Liga, I just imagine he'll have a torrid time vs attackers with pace and he's not the best positionally as I'm sure you know. Ramos is hit and miss, I suppose he can have a good game, but I think vs Bale he's far more likely to have a bad one.
Not really, Marcelo is just doing a Bale, horrific in defence, like against Barca, he was epically awful, he still consistantly throws himself into lunging fast tackles that take him out the game while missing most and leaving whoever he was trying to tackle miles to run into. Take them out of defence and well, you minimise the worst part of their game hugely, push them forwards and the strongest part of their game gets easier. If you're running from left back you've often got further to run with more defenders to beat and more time for dm's and spare wingers to crowd out that right back position. Starting further up, with their pace they often only have the right back to beat, higher up the pitch with far more room in behind, as both of them love the kick it long and run after it with speed tactic, it just works hugely better from left wing than left back.
He's only better in attack as he's played quite often at left wing instead of left back, freed up of spending half the game making defensive mistakes he gets further forward more often and starts from higher up the pitch, that naturally improves you going forward.
Unfortunately he's inconsistant, for every game he bundles through and scores a wonder goal, theres 5 games he'll shoot consistantly from just about anywhere on the pitch with hugely better options he ignores all around him, in either situation he's rubbish defensively.
Infact, he really is very similar to Bale, he's just pure energy, and hugely strong which gives them both that run down the wing and have people bounce off you effect, kick ball, run after it, outmuscle people trying to stop you, and shoot a heck of a lot.