Regarding the bolded, it's my belief that being a central defender in such a system isn't something any defender can do. Yes, possession is key, but the back line is an integral part of keeping that possession. And any mistake made while on the ball is deadly, as the opponent has a free lane to the goal. If you're playing for Barcelona or City (the only other side which uses possession this way), you need to know how to hold the back line extremely well. How do you handle balls over the top? How do you set offside traps? And don't forget that despite holding possession, you'll need to defend corners, indirect free kicks, long balls into the area... it's a vital part of any team that has desires of playing this way. And I feel that specifically with regards to Pique, to the contrary, such a system has exposed him at times when he wasn't in the best of form (2012 comes to mind). If you're shit, or even mediocre, you will stand out in such a team, and not in a good way. Simply for the fact that under pressure from the opposition, you are unreliable as an option for the pass.
I get the temptation to think that Pique has had an easier job compared to Madrid defenders... I won't argue the opposite, I'll just say he's been an indispensable part of why Barcelona haven't conceded as much as Madrid over the past 10 years (of course in addition to the possession and all that).
I've asked this before, and with no disrespect to Ramos, is there any significant gap between Pique and Ramos (apart from goalscoring)? I can't think of anything that would make me put one way above the other, non-goal-scoring-wise