I think it’s been known or assumed for a while that all the x-wing helmets were going to be based on the rogue one props, as far as producing these it’s easier to just have one mold to do the different paint schemes I’m sure.
As for the shapes and sizes between the different films, yes I think the rogue one helmets are considered to be a different shape- I have the Rey anovos helmet and an RS, and they are not the same at all (anovos is significantly smaller). And as for the TFA Rey helmet I thought I remember reading either here or Rebelscum that they may have repainted an EFX Luke/Wedge helmet, but don’t quote me on that.