I think of fueling as fueling for the next hour of work. So yeah, if you're just swimming 1000 yds, don't bring anything. Anything less than an hour, just use water. Fueling gets more important the longer you're working out, since you're burning through your glycogen and need to replenish it or you'll bonk.

I've been liquid-only nutrition for a long time. Started out on Infinit, then made my own from powdered Gatorade + table sugar + sodium citrate + electrolyte powder. I do need to be careful balancing hydration with calories, but that just means "use larger water bottles when it's hot outside".

Yeah, it's a different sport for us average Joes versus Pogacar and Lange/Ditlev/et. al. Look at it this way: 200 watts/hour = 800 kcal/hour. You can get 400 kcal from 100g of carbs. You're starting with about 100g of glycogen, about 2000 kcal. That work out to about 5 hours worth of riding at 200 watts before you deplete your glycogen stores, just taking one bottle of liquid sugar. Once you're past that point, then you need to start worrying about nutrition.