Retroactively charging developers, that's stupid.
However, I'm not knowledgeable on any Game Industry economics, but isn't $0.20 on a $20-$60 game negligible? I understand some people will have multiple devices so the developer could be out $1. On a $20 game that someone sells 1000 copies, that's only $200 of $20,000 sales (maybe $800 in fees at the high end). I've used Unity before and it's still a pretty solid game engine with easy to use tooling; using it would definitely save you time to build your game (time=money). Additionally, if I were to be building a game studio, everyone knows unity, so it would be easy to hire or find contractors who can help with pieces of the game. It makes sense from a business standpoint for me unless I'm missing something.
Is there a max fee? On the opposite side of the spectrum I could see DDOS-like attacks on game developers where an attacker can spin up a bunch of virtual machines and then keep installing the game to charge the developer $1mil dollars.