The standard in the PL is City, who last season had all of KDB, Foden, Silva, Doku, Grealish, Alvarez, Kovacic and Nunes rotating through their attack/midfield across different competitions.
In that context I'm not sure it makes sense to strictly think of the team in terms of "first choice" and "rotation options". Because the odds are total minutes between some players in both categories will be pretty comparable.
Especially given The Athletic reported that Jason Wilcox pointed to the high number of minutes young players like Garnacho & Mainoo were playing as a problem in his conversations with ETH. If the expectation is that we rely on those players less, that means more minutes for other players.
If Mount stays fit then over the course of the season he will get a lot of minutes, likely in more than one position. And, given the type of player he is, it would hardly be surprising to see him crowbarred into the team in some big games either where the emphasis is on pressing, work-rate and tactical discipline. At which point the argument that he isn't notionally in our first eleven isn't particularly relevant. The better measure is total minutes across the season.