Actually what we are discussing has been experimentally determined and modeled. Whether we are dealing with a bullet, the X-15 rocket plane, the Bell X-1 or the Space shuttle the issues and physics are the same. Because the bullet is a passive projectile it does not have a significant flight time therefor the amount of heat it absorbs is limited.
You may find it interesting that the Bell X-1 rocket plane's fuselage was modeled after the 50 BMG bullet which was know to be stable in supersonic flight. The Bell X1-B was equipped with instrumentation to measure aerodynamic heating. This experimentation occurred during the late 1940's to 1955. This provided an enormous amount of knowledge about supersonic flight up to about Mach 2 (2250 fps).
In the late 1950 through 1968 the X-15 explored the high supersonic low hypersonic region up to Mach 6+ (6600+ fps). There were addition X planes later, many of which were used to investigate drag/lift characteristics of various shapes.
As to whether or not the tip used on the Hornady bullets actually deformed is debatable the fact exists that there is a mechanism that can expose the tip to temperatures high enough to soften many elastomers/polymers. The desire to achieve a high BC drives the desire to achieve as pointed a tip as possible but that desire increases the likelihood that the tip will melt due to its small mass and the fact that the stagnation point may actually occur on the tip. I will say that the release of the Hornady information came at a time that bullet manufactures were concentrating on long range bullet capability and thus it is reasonable to expect that this problem could show up at that time.