The words Trent and Alves should not be put in the same sentence ... ever. Trent is good at crossing. Alves mastered all aspects of being a full back. He made the whole right side his own.
Marcelo is not even close to GOAT level either. He's only had 4 years max at a high level and even those were nothing ground breaking. Compared to a player like Roberto Carlos , I don't see any facet of football Marcelo does better tbh.
It's also clear that Alba has been more consistent, more successful and just as good in his prime if not better.
Alves wasn't even a RB really, he was a #10 who just fancied playing from the back. He played striker several times for Sao Paulo this season. He's just a great attacker who can play pretty much anywhere bar the left side.
Carlos said several times Marcelo's levels above him in terms of raw skill. Don't really see the reason to argue, it's clear to anyone who watched either of the two play who's been a more influential player during their time. Alba is probably the only guy who comes close to Marcelo in terms of being an MVP playmaker left back. As defenders many were better than any of them, but you'd never pick them to win a game of football. Marcelo is in the very same mould as Alves, but less systematic.
Not sure of the point of ranking one over the other. It's like saying Ronaldinho wasn't a GOAT level talent because he performed for 3 seasons and got bored. Or that Ronaldo wasn't one because of his knees and having weight issues.
[MENTION=26762]Copperpot[/MENTION]
It really is quite common to have fullbacks register key passes in teams playing any iteration of 4-3-3/4-2-3-1. Again, if he has more key passes, he probably has more passes than many midfielders. Not that unusual on that level. It's part of Liverpool's success given their midfielders are mostly brute grafters with inhumane endurance, but you don't really want them to be on the ball all that often.