The problem with Cancelo at left back is he isn’t left footed, so has to keep cutting in on his right - which has two negative impacts which are very difficult to mitigate.
Firstly, it narrows the pitch - which Pep hates (Sane’s inability to stay out wide was one of the main reasons Pep stopped playing him, despite his upsides), which makes it easy for teams to pack the middle as we don’t have the capacity to play around them so have to try and play through all the bodies. Villa did this very effectively the first half on Sunday, which was partly why we looked so shit until Prp switched it at half time.
Secondly, it forces our left winger to stick to the touchline in an effort to widen the pitch all on his own, meaning he’s too far away from the goal to be as dangerous as we need him to be for the way we play. This means, as good as Cancelo is as an attacking fullback, he limits either Foden or Grealish when he’s playing on the left - who are way more capable of scoring and creating goals.
We need to keep him on the right, and get him used to that position in our team - where his upside is much more exciting.
That leaves Zin - who as we all know is a midfielder very capable of playing left back - but he has his limitations, and is susceptible against the best sides.
For a team at our level not to have a proper left back is ridiculous. We’ve made do exceptionally well over the last couple of years whilst the Mendy disaster show rolled on - but just like our lack of centre forward, it’s a position that needs addressing if we’re going to beat the very best on a consistent basis.
If we want to talk imbalances, then buying a third right back would definitely fall into that camp!