I reject your reality, I substitute my own !!
But it's obvious he was bought mainly as an inverted LB here as the rumours surfaced after Martinez was too expensive. I counted Zinchenko games as LB in City and it was like 98%.Zinchenko was signed by City as a midfielder and fit in as a LB because of injuries. For Ukraine he plays as B2B midfield as captain. City sold him because he's defensively fragile because he's not really a left back. City fans don't consider him a left back.
Inverted fullback role is not the easiest, so you would need to have a good suggestion for LB because Tierney is so injury-prone.
It's easier to find a proper CM in this market imo.
We will likely play Zinchenko in easier matches and Tierney against tougher wingers when both are fit.
City sold him because Zinchenko wanted more minutes and they thought they can get Cucurella. Now they have prospect Gomez as 2nd LB. Not sure City fans are happy with that switch.