Okay, this right here shows you don't know what you're talking about, in a Dunning-Kruger sort of way:

Since calories are a measure of heat energy, they are a reductive measure when it comes to nutrition. Much better to think in terms of nutrients.

Yes, calories measure heat energy. No, they're not a nutrient. However, that doesn't make them a "reductive measure." Nobody (at least, no one who understands nutrition) is talking exclusively about calories. It's part of the overall picture.

There are three main macronutrients: carbs, fats, and proteins. Each one provides calories. When your body uses energy (which it always does, even at rest, but uses more during activity), it needs to replace them. A caloric intake requirement measures how many calories you need to replace the energy you burn during the day. Nothing more. Any attempt to apply it to something else, is misinformed at best. ("I can't eat that, it has calories." Bullshit.).

Also:

Stated another way, there is no such thing as an essential carbohydrate.

There's no such thing as an essential protein, either. There are essential amino acids, which build the proteins. There's no such thing as an essential fat, either. There are essential fatty-acids.

"Essential" in nutritional terms refers to "building blocks," not "necessities." If you're applying the latter definition, then that would make fiber an "essential carbohydrate."

Lastly:

The body is able to use the glycerol backbone from triglycerides to make glucose, alongside several other things like proteins and lactate

Yes, it is possible to make glucose from other sources. I never denied that. I said it's impossible to do it exclusively without serious consequences.

If all of your caloric intake (yes, I said caloric, because that's what we're talking about. bite me.) is coming exclusively from fats and proteins, you're going to have medical issues. That doesn't mean it's impossible to get energy from fats and proteins, so stop arguing that point because no one is arguing against it. In fact, it implies that it is possible. How would you get medical complications from something that isn't possible?