Except straight up cloning a game takes a crazy amount of work, and making something similar with your own ideas is what the overwhelming majority of progress in gaming is.

I’m not saying this game is or isn’t worth it, but it absolutely isn’t unethical in any way to do your own version of a game you like with your own opinions on how the game should work shining through. Complaining about this is comparable to the guys who sued epic thinking they were entitled to the battle royale concept they didn’t invent.

You own your complete package, and your assets. You don’t own the concepts inside it.