Again, we had both starting CB's returning, but we were losing one of the starting strike duo. Yes, Kompany was injury prone, but so were Aguero and Jovetic. This feels like dejavu.
Put it this way, both positions were losing something. Striker was losing a starter, CB a backup. Both positions had injury prone (or deemed injury prone as the case turned out for Sergio) stars. And our defense actually got much stronger towards the end of the season as our goals dried up. I pointed all these out in many arguments I had back then.
The interest and believe that Mangala was the better choice was a carryover from the previous January window needs, when we had been scoring for fun and seemed weak on defense. By seasons end, Demichelis play had jumped leaps and bounds and Garcia was playing better. Where we had actually dipped in performance was at scoring. Post Negredo injury.
Sanchez, outside of being world's better than Mangala, was actually a greater need by season's end. But because we went in for Mangala in January and failed, folks just believed we had to have him in the summer.
Again, I pointed it out then, that if everyone was healthy, Mangala was going to be a backup his 1st season (Even if he developed into world class) on the other hand, Sanchez was going to start immediately in our attack. How is a backup more needed than a starter?
MDM did improve in the second half of the season and was an important part of our finishing second to the Scousers. But no way could he be considered our primary option besides an already creaky Kompany given our goals. Nastasic was well out of favour by then (and arguably rightly so after a poor season), so we were very thin at CB. As for goals drying up, we scored 156 that season, smashing the record and including plenty towards the end - remember even with Aguero out, Dzeko stepped up incredibly and Yaya was on fire the whole season. Virtually all the games we lost were due to rookie defensive mistakes (e.g. Hart/Nastasic fuck up at the Bridge, Kompany at Anfield, the Cardiff and Villa fiascos). Can obviously argue anything in hindsight, but it's a major stretch to say offence was our problem after that season ended.