Really?
BMX raceing just looks like a case of being able to jump, then being able to jump big jumps (which is just progression of the same basic skill), and then the rest of their training seems to consist of gym work, velodromes* and raceing. From a skill perspective I reckon competative MTB is far more demanding with big jumps, and corners, drops, steep bits, climbing, etc etc, not just jumps and bermed corners.
*which to me look like harder work from a skills perspective.
Pro XC MTB’ers are a bit nuts, I remember riding the Seagull run at Swinely (which isn’t that technical, but is quite tight and twisty with plenty of off camber bits and a few ditches to cross) and being overtaken by a team of guys in head to toe Giant kit, they must have been doing 3x my speed, and riding it tighter than a team pursuit! No fuss, no drama, no skidding, they just rode everything at full pelt.