You are making a splendid job of these horse paintings and I admire the way you are looking at the anatomy of these Thoroughbred Horses.
You are quite correct and yes the Thoroughbred Horse's body and legs is like a stylized athletes body...sleek and long and built for speed! All horse breeds have slightly different body mass etc. It would take a lifetime to study each horse breed, and of course pony breeds are different altogether.
(I do think maybe you have lengthened the neck and bent arch of the horses neck a bit too arched, making it look more like and Arab....but that's just being picky, and it's your painting so you can do whatever you want to with it, so don't worry about it!!!!)
There's no-one more intensely critical than another horse person about painting/drawing horses! I've drawn and painted horses all my life and still don't get them right, so you need to congratulate yourself on making a great job of your paintings! I love them, so do please keep them coming!