The initial argument was that putting Rovanpera full time in 3rd car lost them manu title in 2020. That stands.
Using Mikkelsen in that seat or using him only for some rallies while Rovanpera drove in an extra car would have given them much better chance.

IMO it's quite hard to argue that Rovanpera's development would go slower if he wasn't nominated on some rallies as long as he would start them. Car availability doesn't seem to be a problem at Toyota (ref Lappi in Finland, Latvala last year). So it was only a question of money and management choice.