I didn’t know about Gamemaker’s newest version. That’s pretty nice actually.
Of course if you’re already familiar with Unreal Engine and it fits all your needs, there is no reason to go elsewhere. I guess that’s also the reason why a lot people still stick to Unity.
But for me as mainly an artist, Unreal offers the better tool-set out of the box. And having a Windows machine now, there is no reason not to utilize Epic’s offerings.
Sure Unreal’s Paper 2D is capable. I wouldn’t say otherwise. Personally, I just find Unreal a bit overkill for 2D stuff, or even Unity for that matter. Eventually those are 3D engines for me. But that is just my own preference.
Your 2D fighting project shows, that you can get something cool done with Paper 2D too.