Or have significantly higher lean body mass than a Tour de France rider, since lean body mass is pretty much a multiplicative factor in energy consumption.

> Tangentially, there are oodles of Youtube videos about the diets of professional dancers... who practice 6+ hours a day... and none of them are even breaking 3k calories.

The thing about being a serious amateur dancer is you can be much bigger (both height and frame) than you could be and ever hope to go anywhere professionally in most styles of dance, which professionally tend to very rigorously filter for a very narrow range of body types (even, e.g., in ballroom, though classical ballet is the most notorious and perhaps the most extreme for this.)

FFMI has nothing to do with having low body fat. It's literally the exclusion of fat from the index. You can have a high FFMI and a high BF%. A few years ago I had a DEXA scan done to assess my starting condition prior to starting an exercise regime. That scan showed me as having 30% body fat at a body weight of 260 lbs. Being 6'2" I had an FFMI of 23.4 and an AFFMI of 22.9. My calculated BMR at the time was in the 2200 kcal/day area. (Might be misremembering the BMR, but it definitely wasn't in the high 2000s.)