Hey–congrats on the epic effort!
I’d say the part of the race (climbing or descending) that beats you up the most is the one you are prepared for the least. That said, with all else relatively equal, it’s usually the downhill, since eccentric contraction is the prime driver of DOMS. Furthermore, your body shuts you down–eg, via cramping–on the uphill well before really severe cellular damage occurs. This cramping response is likely neuro-muscular, and not just electrolyte of hydration related. Downhill seems to be mostly limited by pain, I suppose.
Here’s a question related to the hamstring soreness: what percent of the race did you walk vs briskly hike vs run? and what percent of your training did you walk vs briskly hike vs run? — ie was your training specific enough during the final few weeks before the event? did you do enough brisk hiking? did you train in the heat enough? Those little washes of water you describe that broke up you rhythm may have also had something to do with it.