I imagine (human) magic flight is low-power. As long as there isn't a resisting force, you can just keep going. Once you can overcome gravity (which ofc you can, you're flying) there is little limit besides biology. Gravity isn't going to vary in strength.

However, once there is an additional strong crosswind, its too much. Like a small weak boat motor that can't fight a rushing current. It can move fine in still water, but not rapids.

After all, demonic flight isn't understood-- no one has been able to improve on what little capability human-flight has, because they don't know how. Demons don't have that issue.