And how much Morgan is in the modern Morgan horse breed?
That also has been diluted and outcrossed many times, yet still, one can recognize Morgan type, movement and temperament, stamina and longevity over 200 years later.
I am in the PNW. Appys are a definitely different breed, not just a color pattern or QH with spots.
If you want foundation, there is the region to explore.
I won’t disagree with you that the genetics might have been severely reduced, but there is such a thing as prepotence and selection and back-crossing.
I didn’t actually find a ‘massacre’ of the Appaloosa herd comparable to the Duro Canyon horse shooting of 1851 after defeating the Comanche.
Instead, references to them being ‘left behind’ (confiscated) doled out to ranchers, possibly officers, exhausted horses being shot, and the remaining stock auctioned off. That auctioned horses may have gone to slaughter in the 1870’s is probable; but useful horses would definitely have been bought up by ranchers and settlers.
It was a different time than today with horses being as valued as cars.