Despite your size you are a true horse neither pony nor miniature What you?

Here's why:

* Despite your size... Thoroughbreds are known for their elegance and athleticism, not necessarily their size.

* ...you are a true horse... They are definitely horses, not ponies or miniatures.

* ...neither pony nor miniature... Thoroughbreds are a distinct breed, not a type of pony or miniature horse.

Let me know if you'd like to try another riddle!