True. Piqué and Alba might not be the best defenders in the world but if we manage to pair them with a great CB and RB our defense will be rock solid again.
Agreed. Pique has to be your weak link in the defensive chain, not your strong link or anchor. He is not consistent enough nor is he fundamentally sound overall to be your anchor. He must be your 2nd CB and have a superior CB by his side that has good cover skills to support Pique when he gets beat or is found wanting on pace and agility, which happens plenty. If he is able to get support, Pique is a very adequate defender, and can bring good performances to the team.
Alba also needs cover. He is excellent intercepting balls and clearing them. His speed allows him to cover space quickly and intercepts dangerous passes. However, Alba struggles a lot 1v1 defending, specially vs someone who displays physicality. He is also a poor tackler, and a fullback needs to be a decent tackler. Alba also needs a strong backline to support him. He cannot be your strong link, else you're going to find yourself in trouble.
I don't know if people noticed this, but usually the backline is Alves-Pique-Masche-Alba. VS Madrid, Pique and Masche switched around. I assume Martino anticipated speed attacks from the right, and switched Masche and Pique around so Mascherano's superior speed to Pique would help out on the right. It was a sound analysis, however maybe the lack of familiarity playing right had a part in Mascherano getting totally destroyed. Alves getting no help to cover his wing also threw that gameplan out the window.
Bottom line though, the team needs some serious reinforcement at the back, among other areas.