Unity isn’t a game engine. It’s a malware-pushing advertising network which merged with a game engine to acquire a delivery channel and now wears its skin. This is fine for the bigger devs and publishers structured around platform relationships, but for everyone else? Gamemaker, Godot, Unreal, Defold… pick a flavor, they’re all on square one.
Even if they are not currently lying and have the magical ability to determine the exact number of installs. They have shown that they will arbitrarily change their pricing structure. There is no way they can be trusted. Anyone who can move their project to a new engine would be wise to do so.
Even if they aren’t lying and have the magical ability to determine the exact number of installs, some asshole is going to create a bot net which spams unique installs for developers they don’t like, skyrocketing the number of “installs” and therefore the cost to do business.