I think Black Panther and Captain Marvel proves they don't need Spider-Man. They can take non-A list characters and turn them into billion dollar franchises. Calling the Guardians of the Galaxy B list would be charitable prior to their movies, but they ended up making a lot of money. Right now marvel has enough momentum and good faith to turn pretty much any franchise into a sucess.
And like I said in an earlier threat, I honestly believe they expected to get rejected with the 50 percent offer. I think that's just how you negotiate. You ask for more than you think you'll get.