Several fantasies just give em required secondary powers. Griffins use wind magic. Dragons use some form of antigravity or flight magic.

Iirc in Stormlight, the ... gigafauna?(Googles and finds it has been cooked for how I want to use it...huh) have gems in them that allows em to sorta reduce gravity in order for them to be able to survive at such a size (the planet also has lower gravity than earth,at 0.7G)