Just because it didn't limit their imaginations to zero doesn't mean it didin't limit their imaginations at all. And again, it's not about having limits on their imagination, that happens with every big film, it's about having to accommodate someone else's imagination as well. Notice, as much as these films all feel like they come from the directors, they ALSO feel like MCU films. That's not limits, that's creative input, and that's something directors have not had in the past.
Might doesn't make right, just because Marvel can doesn't mean that they should. Just because there are positive results doesn't mean there are no negative ones.
In the history of cinema, it's been the director's vision and then the actors touch, with the studio providing funding and choosing someone whose vision they like. The director has been the chief creative officer. In the MCU, and only there, he is not. He's like that VP that does all the work but the President shows up and takes the credit.