the problem with this thinking is looking at your ‘excess’ fat stores like they are just some secondary gas tank that you can draw from without any other effects. Your body sees fat as a protective mechanism from future food insecurity (a huge evolutionary problem) so it won’t just let that fat go and not try to get it back. When you start to empty your fat cells they signal that emptiness through hunger, low energy, etc.
You’re right in that the more overweight you are the more wiggle room you might have and the more weight you have to lose the higher calorie deficit you can manage. But it’s not by that large of a margin and especially if you are training with any sort of volume or intensity you are limiting your ability to recover if you are consistently getting into the 750+kcal deficits.
You can also get into a situation with very large deficits where you body looks around and says “damn I’m not able to get all the food I need to get, meanwhile I’ve got all this muscle sitting around requiring a ton of energy just to maintain. Why don’t I get rid of some of it?” and you can start to lose significant amounts of muscle. It’s just so metabolically demanding that if you aren’t lifting consistently and not fueling enough it will start to get rid of it. That’s how you end up with lots of recreational endurance athletes who don’t lift that are ‘skinny fat’.
Yeah, I understand the rational line of thinking. And it probably does work decently for people who aren’t riding too much or too intensely. But your body doesn’t see fat as uselessly as we do and it won’t give it up so easily.