That is indeed why you don´t see them collapsing and also why the finals are much longer nowadays. Riders train their guts to be able to eat up to 120g of carbs per hour, for the whole duration of the race.
When I started the general guidance seemed to be about 200 calories (50g of carbs) per hour during training and races. I followed that or a little above for a long time, and constantly had problems both physically and cognitively near the end of races.
It took about a year to get used to fueling heavier (for me...about 400 calories per hour or 100g). Lots of figuring out digestion and timing and sources and other factors. But once I got there it was transformative...I could push much harder for much longer without a deep bonk and recovery was faster. More importantly, my ability to think/plan/make decisions at the end of races was orders of magnitude better.
I'd bet if you went to an aid station around 80 miles on a 100mile ultra marathon you could pretty reliably identify who had been on the 200cal end of the spectrum and who had been on the 400 + end.
These days I cram haribo and peanut butter M&Ms, although I think the latter are more useful for multiday things.
Edit: I did the math on that risotto cake recipe and it comes out to about 2500kcal for the batch, for me that comes out to calories for ~5-6 hours of riding.
I did a similar ride a few years ago, I mixed gels, energy bars with bananas, nuts, sandwichs, nuts and pastries bought along the way.
900-1000 calories might mean that in is optimal - but think about eating a full meal from mcdonalds every hour while massively extering yourself.
Training your gut matters and I've never seen anything that suggests much beyond 400 calories per hour is possible during meaningful exertion.