Yes but you wouldn’t actually need to make your clone very different for the copyright to be entirely different and then surely you wouldn’t get sued?

Are you confident enough to bet 6-12 months of dev time and resources(possibly lawyer consultation fees) on that assumption ? because up until recently that's what someone would need to do to find out.

It might be fine, but the threat of litigation is a part of the deterrent.

But also you can’t really copyright UI beyond the design itself, the functionality is free game as far as I understand.

As with all of these things, it's region specific.

However, game mechanic patents and copyrights exists and are litigated regularly.