I think it's totally fair. I don't know if this is the right take here but I think we as gamers have limited power in this situation as we're not really Unity's customers. It's the developers who have the power to move away from or limit their use of Unity and pressure them to change this decision especially as good alternatives exist already in the market. I know this doesn't help for existing games but hopefully they can at least get Unity not to make these fees retroactive, seems legally questionable to me as a layman at least.

Maybe one easy thing us gamers can do is to block unity domains at the network level. I'm not sure how they track installs but I'm guessing it must include some kind of phone home.