The reality is many of us simply don’t have the time to do long rides that simulate the duration of such long races like Leadville, but that doesn’t mean we can’t do them.
I think it’s important to note that David isn’t the only example of this, and this isn’t something unique to TrainerRoad.
It’s key to remember the nature of the effort during the race and the things that will be performance limiters on the day.
Longer races, if paced judiciously, are almost entirely aerobic in nature. Although this is a simplification of a complex thing, remember that even up to 120% FTP is still technically predominantly aerobic work, meaning there are many ways to train your aerobic system. As long as the intensity and duration are well managed, you can bring about significant aerobic training adaptations with short sessions that will still prepare your aerobic system to do something like Leadville.
That said, no matter how aerobically fit you are, bad pacing on such a long day (and high elevation, in Leadville’s case) will be a serious threat to reaching your goal, or even just finishing. Same could be said for nutrition, basic strength to be able to hold proper positioning all day, and even equipment choices.
So the direct answer is, you can do a lot of quality aerobic training with 2hr workouts that will prepare you for long events like this.
Will you set the course record with just 2hr workouts? No. But it has allowed goal-achieving performances from plenty of athletes at many events.