But presumably Marvel must have some creative input into the Sony Spider-Man films They wouldn't just let them do anything that might potentially harm the bloated cash cow that is the MCU.
There will be creative input – the next Spiderman film, I believe is being produced by the head of Marvel Cinema and his team. This makes sense, rather than being a necessity.
With what you said, I think the other way round would be better - Sony has the rights, not Marvel; it’s not up to the latter (or rather Disney) to dictate what Sony can or can’t do. Both parties have something to gain by this deal and if Sony did do something, for instance, to damage the Spiderman brand, it’s shooting itself in the foot. I don’t think Marvel have too much to worry about there, but there are going to be clear benefits working together to
maximise profits make the best damned films possible.