answered:
What, you thought ponies could just fly because wings? No no, those wings could never possibly support the body structures of the pegasi that use them, especially someone like Bulk Biceps.
It was pretty much confirmed in the Season 4 finale that Pegasi’s ability to fly is magic. The conduit for that magic though IS their wings. If their wings are damaged, that magic connection is severed until the conduit is repaired. And they need both wings to obtain flight and use weather magic.
So yes, Pegasi flight magic.
Just like if a unicorns horn is damaged, they lose their connection with magic.
Remember when Shining armour got horn herpese from sombra?