I don't necessarily disagree with anything you're saying, but for Universal to give up the Marvel attractions, they would likely require Disney to buy them out -- that means $$$ for demolition and removal of the Marvel elements as well as $$$ for development and installation of the replacement experiences. They may even want a premium for the inconvenience and/or something to make up for the loss of the valuable Marvel IP. It would be a massive, massive price tag that I'm not convinced Disney is willing to swallow anytime soon, especially when the company is short on cash and already planning to invest a significant amount in other areas. Universal has shown a willingness (and legal ability) to update its Marvel attractions in the past few years with the rebuild and rebrand of Hulk.
As for Oswald, that was a dormant IP. Universal was likely more than happy to trade it for something they did want and could actively use.