I see your point, and even somewhat agree. I hate the thought of a director's creativity being stifled. But I also feel like this is a very unique and tricky situation. If Marvel is to continue with this shared universe concept, and if the characters are going to start appearing in each others' films more (instead of it always being merely Fury) as I suspect they will, then character and world-building continuity (tonal, emotional) is going to have to get significant focus. These films are not meant to be
completely individual pieces of art, so it seems almost counter-productive to me to treat them as such. IMO, this series has the potential to be something completely new to cinema - like I said, it could be like a television series on an exponentially larger scale - where the whole becomes the main attraction, the individual work, more than the pieces. That's not to say the solo ventures can't be individual visions on their own, which is why Whedon would be the perfect man to oversee this instead of someone more driven by the commercial side of things like Feige - because Whedon knows how to create memorable and unique episodes that also serve a greater story. With
Buffy, the "big picture" was just as much a work of art as some of the individual episodes. Sometimes I think Whedon just gave some of his writers a basic premise for an episode and said, "take it and run with it." I feel like he could do the same thing with the solo films of this franchise, while ensuring that whatever they come up with still serves the bigger story he's trying to tell in the MCU.
I know, I know, it's a radical concept that's unprecedented for many good reasons (like the one you presented), so I'm sure it would never happen. I just think it would be kinda cool.