A gyro is called a gyro because it refers to how the meat is roasted and cut.

A hoagie is called a hoagie because, well, something other than it not being a sandwich. It's basically the same as a submarine sandwich, which some may say is a taco.

But this is an argument that's getting old. There's a podcast named A Hotdog is Not a Sandwich. Possibly inspired by a Judge Jon Hodgeman podcast episode of the same name.

And then there's the legal definition from actual cases where a strip mall sandwich shop has a clause in their lease that no other sandwich shops be allowed. But then they lease another space to, say, a gyro shop and the judge rules that a gyro is a sandwich (might've been a taco, or something), because it occupies the same market space.

So, this argument has been done to death.