IMO the problem is more the arbitrariness of the change than the specific fee structure. It applies to games that are already in development, it applies to games that already shipped. Even if it's strictly legal to pull that rug (I have my doubts), no one wants to build a business at another company's whim. Everyone is wondering if Unity just turned X% of their customers into sharecroppers, who's the next Y%? For indies that will be an especially acute concern since they have very little leverage.
Better fixes in no particular order: a grandfather clause, delay the new fees, fire the CEO.
Would it be any better of it there was retroactive revenue share? I agree it is shittily rolled out, but things like the retroactivity are the issue, and the ability to actually count install. Not the install fee itself. I am responding to the "it should have been rev share" mentality, which is totally grass is greener.
Better fixes in no particular order: a grandfather clause, delay the new fees, fire the CEO.