I agree. It is also a waste for Kyojin (I mean as soon as you take a rookie, you need to give some time).
The question is, how much you think Ropz is better right now. If you think they are already close to each other, then sure, keep misutaaa.
But if you think Ropz is a top player, you have no garantee that Misutaaa is going to be as good as him, even in his prime. So from that point and if you want result now, as it seems the case for Vitality, you make the change.
I would have personally keep the french roster. I Like them, and want the young one to develop !
But as soon as you kill the project and go international, you need to make the rational choices. Maybe Misutaaa is seen as a very very good player that have more potential than Ropz. Maybe not. I'm no expert.