Agreed, it's the aerobic engine. I think many racers do too much intensity and don't focus on the lower end aerobic base enough. Even 2x20s imo are typically done too hard by many (probably because of skewed FTP due to 20 minute tests). It shifts the balance of where the power comes from. If you've developed the anaerobic component, you can hit a good 20 minute power and think you're fit, but if two riders can do 300w for 20m, but rider a develops 80% of it aerobically and rider b develops 65% of it aerobically, then rider a will have a huge advantage at the end of a long race even though their FTP might test "the same." Per my understanding, that advantage even applies to shorter events like crits, because I believe some of the same aerobic components are also responsible for "recharging" your sprint, so if you're maxed out aerobically then you'll be hitting smaller numbers at the end of a crit than you would with a bigger aerobic base.