The fact is that, right now Rodri is at unreachable level for Kalvin. That's why Pep rotated Rodri with Gundo or Bernardo when he needed to rest him.
So Kalvin starts his career from the scratch, which means that he will have to go through phases of professional football career - step-by-step again and convince Pep, that he deserves to play in this City team.
No one cares about his Leeds period or caps in England team, that's in the past.
But there are some positives: Pep's new 4 CB system needs one player who can play both in Defensive Midfield and Centre Back zones.. So this kind of player doesn't need to be as good as Rodri for example and have pace and ball-controlling skills and etc. and doesn't need to be as good as Ruben, normal defender also counts.
Yes, there is John Stones as a regular starter, but there are plenty of games and Kalvin will have a lot of chance to prove himself and contribute there.
That's maximum what we can get of him during the next season I think -> player who contributes from that "Stones" position at the level of John and helps Rodri in midfield as well as Ruben in defense.
After that when he has played a lot of games with City and has experience and practice with the boys and knows system, we can talk about - rotating him with Rodri, i.e one year from now.
As for Rodri - I guess Pep will use Kovacic or Rico, considering both Gundo and Bernardo are gone.
That's why I still think that Rice option is good both for City and Kalvin.
City gets player who rotates both with John and Rodri (Kalvin can be rotated with John only (if we are realistic..)
Kalvin doesn't have to go through above mentioned "cycle of trust" and get a regular starter role at West Ham on that DM position.
But if Kalvin stays, I think there is potential that in 1 year - we will get a player, we signed 1 year ago :D