Explain why you would have a sadly regressing Cancelo over a quality, naturally left sided player like Tierney who has been injured but now getting back to his previous level?
"a sadly regressing Cancelo"
You are projecting temporary problems wrt form on his entire future career, problems inflicted at least partly by the manager due to injury problems of the other FBs at the club. I think Cancelo will regain form in several weeks.