I think that the Shetland ponies are worse to bite. The Shetlands I was around were mean. They would bite like a bulldog and kick if you got close enough behind them. Their saving grace was that they were not big enough to hurt you.
I have a ponytail-pulling Mule. I try to never turn my back to him. He’s just playing, but he can easily yank me off my feet when he wants to. ;)