I don't know if this answers your question, but hopefully it is helpful. Some of it I'm sure you know, and I hope you don't mind me restating it.Why do you include protein in your calorie count? I thought the point of protein was building blocks for muscles, skin, hair, fingernails, organs, semen etc etc. If that is the case, which I believe it to be, why are we advised to include protein in your TDEE?
I think the simple answer is that calories are kind of a proxy measure. The calorie we generally refer to is a kilocalorie (also referenced as a Calorie, with a capitol C), or the energy required to raise 1kg of water 1 degree C - it is a unit of energy, but not really exactly what the human body "sees."
Most often the calories in food are determined by something called a bomb calorimeter, where the amount of heat is measured as the food is burned. Most often the calories in a specific food are calculated - I don't know about other countries, but in the USA there is an FDA-approved database and things are just calculated from that. So if you eat a Snickers bar, and look and see it is 100 calories in a bar, what you actually are looking at is the company that made it calculated how many of everything was in the recipe and then portioned it out into the number of bars 1 recipe produced.
When you look at any food, or all food, your body does not "see" calories like that. In fact, if you look at any nutrient, there is a "cost" to metabolizing it. Depending on what you are eating, your body does not get a 1:1 of energy in : energy available. You might lose 20-45% of the bomb-calorimeter determined energy value - you eat 100 calories, it costs 20-45 calories to process that, and you have available 55-80 calories. But this doesn't mean that you should account for that in planning your diet, as it is often already "built in" in the total daily energy intake value ranges we are given as starting points. (And this is important to keep in mind - the calorie number a calculator spits out is a starting point we adjust from based on results and goals, not a writ-in-stone real-life value.)
The benefit though of looking at calories is that it gives us a language to evaluate and talk about. Scientists have found in things like metabolic wards that we can, in general, calculate the energy demands of the body in these proxy terms. Using calories is a short-hand language we use, but it is crude, as every Snickers we eat or even every 1lb of meat we eat is not identical, there is variance, as well as our ability to account for it in our diet. You plan to eat 2000 calories in a day, and maybe one day you get 1800 calories and another day 2400 calories, even if you think you were "perfect" and nailed your goal.
This is why calories are a guideline with managing diet, and you evaluate and reevaluate based on weight change/goals. You do a calculation based off of all these scientific calculations and it says to eat 2500 calories to lose 1lb a week, but when you do that you lose 2lbs a week. You adjust up and maybe settle at 2800 calories to lose 1lb a week - it doesn't matter if that is REALLY 2800 calories, but if you're consistent with how you assess that and track it, you'll get consistent results.
Another way of doing this is assigning macronutrient intake goals - e.g. 200g protein, 200g carbs, and 100g fat. This would be - if burned in a calorimeter - something like 2500 calories. If you lose weight, or gain, or maintain, you can adjust based on your goals. You don't NEED to calculate calories, but it can allow us to be flexible if we like tracking - e.g it allows variances from day to day as we eat "in real life" - e.g. one day you eat 150g of fat, how do you adjust to accommodate that 450 calories? If you are using calories, it "simply" means to eat 112g less of protein and/or carbs - so we could eat 200g protein, 100g carbs, 150g fats and be close enough. If we took away the calories from the discussion because they are "just" proxies, we needlessly complicate it. And we can ignore protein entirely and just say we get 1700 calories from carbs and fat - but it is the same thing, essentially.
The "problem" with not calculating protein in TDEE is more practical than theoretical. If you say you need 1500 calories of non-protein food, you now have to separate every food into calories and what macro attributes them. 180g of chicken is not JUST 60g of protein, it is also so many grams of fat. You can ignore that contributor, but the more "complex" the food, the more complex the "problem" - solvable, but a lot of work. I eat a slice of whole grain bread at 120 calories, but it has 6g of protein, so now I have to think 120 - 24, or 96 calories. If all you eat are largely single-macro foods (very lean meats, butters, veggies, etc.), maybe this isn't all that challenging. Oy imagining having to do that seems to me to be an over-complicated headache, but hey rock on if you like that sort of thing. The "problem" is complexity and having to recalculate all of the energy calculations, which means you are STILL using protein calories, just on the backend. Does it really solve anything if you say "I need 3000 calories, but I'm going to eat 200g of protein, so I only need 2200 calories + 200g protein." ? How does it simplify things over saying you need 200g protein / 250g carbs / 130g fat ?
When we use total daily energy intake in combination with macro goals, we have something relatively easy to use and adjust, as well as something fairly adaptable to a large range of intakes. Again, this may be more or less helpful for you based on your lifestyle.
Even calculating macros and calories effectively and consistently is "too much" for most people, which is why various other alternatives have been proposed - such as the MyPlate Guidelines from the US Gov't or the Precision Nutrition Hand guidelines. Developing more complicated means that requires more work for the individual may not be useful for most people. Again, it might not be all that more complicated if you eat mostly single-ingredient foods that are also mostly single-macronutrient.
But as with most things involving diet and exercise - find something you enjoy doing that you can do consistently that gets you closer to your goals and employ that. Often, but not always, simple helps with the consistent aspect.
This is a highly contentious topic as the low carb folks (e.g. keto, paleo, carnivore) have their thoughts on how to manage this. Attempting to side step that, my understanding of the science says that the average individual who is active/athletic benefits from up to about 1.6 - 2.2 g of protein per kilogram of bodyweight, or about 0.7 - 1.0 g of protein per pound of bodyweight. Some of this may trend upward as you get older or have digestive issues (NOT MEDICAL ADVICE) as there seems to be some evidence of protein metabolism becoming less efficient in older populations. My understanding of this - largely based off of Alan Aragon's work, which you can get a FANTASTIC summary of protein recommendations in his Protein E-Book or a summary of nutrition recommendations in his Flexible Eating book - is that if you are eating more than 2.2g/kg or 1g/lb, then you are eating "extra" protein (calories) that could be coming from a different (cheaper, more variable) source. For me, this means trying to get somewhere around 160-220g of protein a day, and the rest of my diet can be "other stuff." If I choose to eat more than this, it "simply" means I eat less "other stuff."In saying that, my next question is, with the above being true, are we consuming too much protein, and some of that is being converted to glucose when we replace it with a spicy herb rice and some seasonal fruits?
TLDR: If I "overeat" on protein, it "just" means less other stuff - and I think Alan explains that well in his books. As far as eating a ton of protein (lets say 400g) and THEN eating your normal calories - well that's not how those calculations were figured, and if you have that much protein, your body does two things - it starts using the protein for energy, and since it is metabolically "cheaper" to store carbs and fats, it does.
I wish lamb was the cheapest around here! That is one of the most expensive meats here. Lately chicken and egg prices have been skyrocketing due to repeated issues with the chicken farms (avian influenza outbreaks I think) and now even pork is cheaper. Beef is still $$ and lamb is $$$.Personally I don't have one. But generally I eat around 1kg of red meat per day, mostly lamb (cheapest red meat where I am) and fish (my uncle is a fisherman and I dabble, always have a freezer full)