Oh very true, little horses are sometimes the best jumpers. My mare was 13.2 and could out jump most 16hh + horses. I also rode a mstang mare who was about 14.2 and she could easily clear 4' and higher.
I am in complete agreement with Allison. There's nothing screaming maxed out to me in those videos. Ponies can be a lot more than people tend to think. My favorite pony in the world (who I very, very much wish I had the opportunity to buy... too expensive though) is only 14.2 (MAYBE 14.3) and I've easily cleared 4' with him. It's all in their heart.