Couple things.

Didn't KMT have a recent article suggesting that the rib damage was done recently--sometime after Carter but before Hawass?

I have fallen off more than my fair share of horses. I've fallen onto jumps, onto hard ground, soft ground, trees & grass. The ground is never nice.

But I have only broken teeth. That was on my sister's hunter, when I had a stirrup leather break & I fell onto the jumkp. I broke my font teeth--and I'd just had my braces removed a week earlier.

However, in a chariot you have many ways of getting hurt. The obvious one--falling out--is probably the one where you're least likely to get hurt. But if the chariot drags you, or you get pulled under wheels, or if the chariot overturns--you're in serious trouble. If the cahriot flips, you run the risk of being dragged & crushed. If you aren't stable--and in Egyptian chariots, you really were'nt--you could fly over the front, land on the yoke & then get run over.

So I can certainly believe that he had nasty bumps, bruises, cuts--and a fatal fracture.