Have you ever seen anyone actually do testing on this topic?
I did a 50mm thing back in the day, 9 lenses... all different, some were around 55, others 45. One was even about 60. I have long since lost all of that testing.
It's an interesting topic and a lot of people don't realize "70-200" is simply the marketing, everyone knows what that means. No one is going to notice that it's a 75-185, even if their previous version was different.
I was first aware of this issue with long zooms way back when I bought a Sigma 120-300mm f2.8 OS. I had high hopes for this lens, the Canon 100-300 f2.8 is a thing of beauty and so versatile. But the Sigma was a worse case of a bunch of compromises that led me to sell the lens a fer months later. The focus breathing was extreme. Even at infinity, it was well short of even 280mm. If I put a 1.4x TC on my EF 70-200mm f2.8 LIS II, the Canon lens had noticably more reach. If I foccussed on anything fairly close, the focal length would drop so short, I had more reach with my native 70-200mm f2.8. Plus the poor AF tracking and hesitiant AF lock, plus the truely awful optical image stabiliser....yes this "lens of dissapointment" went back. it was not worth the size, weight and cost over the Canon EF 70-200mm f2.8 LIS II with a teleconverter. Unlike the more modern and better engineered Canon RF 100-300mm f2.8 which is just amazing and really delivers on that particular focal range and brightness.
I often choose a EF 135mm f2.8 L prime as my light weight travel companion instead of the far bulier 70-200mm f2.8. This is because it looses less focal length at MFD and the diffrence between 135mm and what's reported as 200mm in a zoom isn't that much. Sure, it's a bit wider but take a step or two closer to the subject and it's pretty much the same look.
Which brings me to a lens that I'm really frustrated with, the RF 135mm f1.8 LIS. It's a fantastic piece of engineering and a remarkably sharp lens. However it's totally missed the point of the previous lens and makes me wonder who or why would anyone buy it over the current RF 70-200mm f2.8 or even the legacy EF135mm f2.0 L which I currently own.
While the zoom has become smaller and lighter, the prime has grown and become heavier and bulkier. To the point that all of the versatility and portability has been lost in the newer RF verion. On paper it's superior in every metric, except that now it's become bloaty and over sized. Curiously, it's now an even more niche lens that the EF version. The old EF 135mm f2.0 was a master piece of unobtrusiveness telephoto shooting. It was like a ninja stealth lens, especially if you took the hood off. The newer lens is massive in comparison and not much different to the f2.8 zoom in terms of size and weight or sheer bulk. In fact the RF 70-200mm f4 LIS is pretty much the same size and weight as the EF 135mm f2.0L, which says a lot about how much engineering has gone into the f4 zoom. It's a remarkable lens for sure. I just wish Canon has kept the original use case scenario for the EF 135mm as it's primary design objective and not just added features and bulk. Yes, it's brighter, it's sharper, yes it focusses closer, yes it's got IS....but look at the size of the thing!
It would be really cool if Canon considers a 135mm f2.0 in their new hybrid VCM primes range. Or even in their F2 lens line up, Canon could easily drop a 135mm f2 and a 200mm f2! The 135's design criterior that has an eye on size, bulk, price and brightness. It could be the sweetest lens of the pick.