Remember when Ontario had a DH race series?When I did 24hr races, it was as part of a team, and mostly for the party. I gave up on them when I became a parent, and sleep became a precious commodity.
I wish I'd done more DH racing instead. They seem like they were more fun, and the skills would have stayed with me over time. The 24hr races are still cross country races, and all about fitness, which you lose over time (or it becomes harder to maintain at any rate) despite best efforts. All the fastest riders I know today (in our 50s) are former DH racers. My theory is the skills you learn DHing pertain to bike handling and reading the terrain, and those stick with you.
Though now that I wrote that out, the really fastest riders I know are now all roadies or gravel riders and have abandoned mountain bikes for the most part. A few of them used to be DH riders/racers.