I see a huge difference in the way the 70K filly wants to, and is trying to, control the cow. The 6K filly is just sort of reacting to the cow moving, and getting into a position she has probably been trained to take.
My guess is that, besides a difference in chutzpah in the two, is that the 6K filly has been trained and worked on a flag, a lot. Flag goes, horse goes. The horse learns to take a position on the flag, then move when the flag does. The horse worked on cattle learns to try to control the cow- and learns to watch/read the cow carefully, and can often learn the chutzpah to boss/dominate the cow. Border collies do this with sheep (and with cows, if they have the bite to). Cheaper filly is reacting and taking a position, expensive filly is reading and shaping what happens- and knows it.
I’ve been on a flag-trained horse. I don’t like it- the cows KNOW when a horse is trying to control them, and when the horse is just taking a position. It is a LOT easier for me to control a cow on my OTTB because (well, when!) he wants to boss that cow. He doesn’t have the catty cutting/show horse moves, but he can turn over his hocks and get where he needs to be fast enough. And if the cow knows she’s being ‘spanked’, she will quit trying the horse and go where you are asking her to sooner. If you are just blocking her positionally (on a flag trained horse that doesn’t care), she will continue to read the horse’s ‘I don’t really care where you go’ attitude, and try the horse more.
I also agree with the ‘make do’ comment. It is entirely possible that the cheaper filly could learn to read and boss the cow- but you aren’t going to do much, even if you CAN help the horse, in working cowhorse without that ability.
I’d bet that the cheap filly, if she had lots of real cow work- where she understood that she had WON, and done something good, when she bossed the cow, could develop into a better horse. But probably not a horse of the caliber of the second one- that horse has some sha-ZAM!
Also interesting to see the breeding. I bred my husband’s ‘just a horse’ AQHA mare to a Dual Pep son 15 years ago. I got more ‘cowhorse’ than I was expecting, and looking back in mama’s pedigree, husband’s ‘just a horse’ traces tail female back to grand-dam “Kitty Buck”.