I got no problem with any of that. I can too go for several hour long rides with only water. But those rides take place at endurance with the occasional dip into tempo intensities. No problem.
I only use the 90g/hour if I am doing threshold work. Where it certainly lower the RPE, and make me able to better push myself at the limit. The 90 grams of carbs does not have to come from “sugar” but rather the 2:1 glucose:fructose. Personally I feel no “spikes”, and no need to raid the fridge after the ride. Dental health is a concern, so I do rinse with plain water for every swig of the “rocket fuel”. I just don’t see a lot of downsides to fuel this way, if it does indeed lower RPE, and you certainly burn the calories you take in (and more).
This is more a question than a comment:
Just because you can turn a big deficit for a long time in a race like you are saying for TRI. Does that mean it is beneficial for training? Why give the body the stress of training & energy depletion, if the goal is to come out on the other side rested and stronger?
Kind of like special forces selection. They break the candidates down to the very limit over several days. Sure some make it. But they all come out the other end weaker, needing to be “re-built”