That's what i would like to see in FM more... Managers using formations that fit their players not using just one formation all the time. For example if they have many injuries in their squad and they don't have wingers for example, they would use a wingerless formation etc...
In a management Sim, that should have already been the case if you ask me...
Yes, managers should have preferred formations, but that doesn't meen that they should use them religiously like no other formations exist, they should have access to all in-game formations...