There’s nothing preventing GCC from having different inlining/outlining heuristics as well as different cost models for versioning based on target.
Unless you control for that, the results are meaningless.
My own tests say that x86 and arm thumb2 are about equally compact and everything else is fatter. But even those tests probably lacked all the controls you’d need to get it right.
Does it actually have that different logic? Because otherwise this sounds like that tired "nothing prevents the compiler to be arbitrarily smart" argument — sure, nothing prevents that except for the fact that someone has to actually implement this smartness.
I know that every compiler that I’ve ever written ends up having different logic for this based on target, for a myriad of complex reasons.
So I would assume GCC landed in the same place as anyone writing a complex compiler.
You would have to do further and other investigations to draw any other conclusions.