I think with us playing with Walker and Delph/Zinchenko for so long in their rather unique fullback roles for City over the years, the others vying for the roles are put at bit of a disadvantage. The team is so used to the way they play with the unusual FB roles having a conventional fullback is in effect 'unconventional'
Cancelo is a very good right back, but it seems sometimes he's caught in two minds having to balance being a normal RB with the weird hybrid role Walker has. Danilo had similar issues.
Mendy for me is a very good left back in waiting (I know I'm alone here). But he's had to adapt to playing a combination of a normal LB role and the inverted role that Delph/Zinchenko have used. (Watch him in 17/18 before the first injury and he was more of a wingback)
I'd guess that over time that as we play more and more with normal fullbacks we'll transition into a team that uses fullbacks more conventionally and the likes of Cancelo and Mendy will have more opportunity to look like the players we want them to be.
My point in all of this though is that in Angelino we have a very useful player who can actually be in the team for transitional purposes. He's an actual left-back for starters, but he has the technique, agility and presence of mind to do something closer to what Delph and Zinchenko did.
I do believe in the long-run if all works out Mendy would be the No1 guy. But until then Angelino has such an important role and I genuinely hope if it works out that way he gets the credit for it.