I made no such assumption, merely stated two facts (i) the RF 70-200mm f/2.8 is not compatible with TC, and (ii) you can't present a rationale for the incompatibility.
Your second statement is not a fact. I can present plenty of rationales. If they are the ones that compelled Canon to design their lenses as they did, is another matter. I have no insight into that, so can only put forward speculation.
For example, as the resolution of their bodies has gone up, Canon may believe sufficient parts of the market do not require TCs any more and therefore they reduce the cost of their development process by dropping it as a design requirement (or more likely, not add it as a requirement - the EF 70-200mm lenses never were on an official compatibility list, we're they?).
I was under the impression that you acknowledged that Canon also put forward a rationale on their own (more flexible in design with large, closer rear element) and dismissed it because it is something a big Company put forward. You mused that assuming an aspect of a design was compromised in order to improve another was Fanboying. And I mused assuming a lack of a good rationale is cynical.
Where does this leave us? Nowhere in particular, I think. Even if I were a Fanboy and you a Cynic, so be it. Sorry for trying to be snarky.
No. I'm looking for a specific & measurable benefit that could be reasonably said to outweigh the incompatibility with TCs.
I think that's where you run into trouble. By comparing full, released designs, it is infeasible to determine how much impact each aspect of the design has on each of the metrics you could measure (resolution, contrast, vignetting, distortion, weight, AF, IS, weather resistence...).
For example, the RF 70-200 2.8 being only ~ 70 % the weight of the EF version or the Nikon Z one is a factor that is probably the result of multiple design aspects.
So ideally you would get your information from an unbiased expert, but I would imagine input of that sort to become very technical and academic and hard to access.
As for your second part, the value of TC compatibility is very subjective. Depending on where Canon takes the resolution of future bodies and whether they release a TC that doesn't portrude into the lens body, it may change further.