Very much agreed!
Back a few years ago we were on the market for a horse to add to our herd for lessons, and we were offered a QH gelding that had been in the Top Ten National Halter quarterhorses a few years back. Excited, we went to see him. The gelding was 16 hh, nearly 1,400 pounds, and so fat and overmuscled that he looked like someone had just dumped him in oil. Not wanting to discriminate though, I went ahead and tacked up.
For one, my saddle didn't even fit him properly. I had to go borrow a girth from a fried with DRAFT horses, and my girth generally even fits our 17.3hh thoroughbred! Once I slip-slided up on his back, I asked for a walk. Sure, no problem. Then a trot. His trot was one of the most uncomfortable things I've ever had to sit. His legs were so small that he seemed to forget where they were, making his trot sort of...'lumpy.' I asked for a simple, large circle. When I did that, he slid off balance, tripped, regained his footing, then proceeded to do a very lopsided circle with his head as high as it could get (not very high, his neck was super short!) and his body in no way round. I worked him for about 30 minutes, in that time I absolutely could not get him to contact me through the reins or round himself. When I got off, he was puffing and sweating like I'd run him four hours, when we'd never even gone past a slow canter.
To say the least, I was dissapointed! He was pretty, sure, but that gelding would never make a lesson horse, much less a reiner, roper, racer, or anything else that QHs were originally bred to do.
We ended up buying this girl- Jasmine, a 15 hh QH mare. A bit funnier looking than him maybe, but muscled RIGHT (a bit thin...but muscular all the same) and a very capable (and marish xD) lesson horse.