In case of Stellaris it is more like you would buy Stellaris, Steallaris 2, Stellaris 3, etc. Each big DLC is like another game in the series. And the smaller ones (like species pack) are completely optional. For me this is an example of DLC done right.

It is not like e.g. City Skylines, that most DLCs just give some minor additions and for a meaningful change in the game you would have to buy lots of them.

Unfortunately they started to play with AI too :-(

I hope they can be held accountable for mistreating those 'transplants" (what an ugly word!) too. But I guess that would be easier here in EU than in USA.