You make very good points, and they are certainly concerns that many share. We should keep these concerns in mind as we go forward and hope that Marvel Studios uses Spider-Man wisely.
At the same time, however, I can't help but comment on how amusing it is to observe how many fanboys who for ages clamored for the return of Spider-Man to Marvel now suddenly are feeling a case of buyer's remorse.
These fanboys should have been aware of the potential drawbacks of incorporating Spider-Man into the MCU, and they should have thought through these issues before they made their demands. But instead, they shouted their demands for Spidey's return louder and louder, and ever more stridently and intransigently, on every message board and forum. Now they finally have their wish, and now all of a sudden, they now start complaining about it and its accompanying consequences.
Now they voice their outrage over the altered dates of other MCU releases, and they worry how Spidey will fit into the overall universe. Well, shouldn't they have considered these potential downsides before demanding Spidey's incorporation into the MCU? They should have realized that there are downsides for everything.
But they now have their wish. And they're still dissatisfied? Too bad. As the old saying goes: You have made your bed. Now sleep in it.