IIRC, Lauren Faust herself said that pegasi instinctively use magic when flying and walking on the clouds.
 
This leaves the earth ponies as the real losers.

@Everyone Who Says Pegasus Wings Aren’t Big Enough:
 
I’m just going to say, it’s magic.
 
In order for a pair of wings to lift the average 150-pound (68 kg) person into sustained flight (not just gliding), the wingspan would have to be around 20 feet (6.1 meters). Ponies would have a slightly easier time, having a more horizontal body plan, but the average pony, even if we take the “little” in My Little Pony as literally as possible, would still weigh maybe 200 pounds (90.7 kg).

Well, RD’s wings in the show aren’t big enough to lift her, so… Meh.  
Drawing looks very good nonetheless.

run, chicken, run!

Y’know, the most surprising thing about this episode was she was never called a chicken once. (Not even by herself.)  
Very cute pic though.

@Lium
 
What he said.
 
Still couldn’t make enough lift.

They’re still not large enough to logically lift her up so I reckon it’s fine.

I don’t argue with people because most of the time they’re right and I’m wrong.
 
So I stay quiet.

You’d think her wings would be a bit smaller, but hey, who am I to argue with one of the best humanized artists in this fandom.