You'll never get evidence that Canon threatened a third party company legally, it's bad for Canon's PR and if Samyang said what really happened it would sour their working relationship. All we can do is engage in inference, and use inductive reasoning to draw a probable premise from the limited objective information we do have. Applying Occam's razor, the simplest explanation is usually the most plausible one. If have another explanation which is as simple or more so, I'm open to considering its likelihood in terms of probability.
I don't understand the Samyang/Rokinon company structure, why it sells under one name in some countries, and not under others, can manufacture RF lenses under one, but not the other. If anyone can anyone explain the workings of this company, many would be interested.
1. Why did Samayang cease production of a perfectly good working lens?
They didn’t. Samyang is the manufacturer. They sell their lenses under different private labels. Rokinon, Bower, Vivitar, Walimex, Opteka, and a few others are all labels for Samyang-made lenses. In the modern era of global commerce, major retailers often sell several of them, but they're the same lens internally, and all manufactured by Samyang.
If Canon had somehow forced Samyang to stop making RF mount lenses, they would not be available with the Rokinon label, either. The simplest explanation is that Canon has not forced Samyang to stop producing RF mount lenses.
RF lenses that are worse than EF lenses for various reasoins, but cost more, that's easy, two come to mind:
RF 14-35mm f/4 L vs RF 16-35mm f/4 L
RF 100mm f/2.8 L Macro vs EF 100mm f/2.8 L Macro
This could be a can of worms, but from what I've read in reviews, I'd rather keep the EF versions, which are cheaper. YMMV!
Having used both the EF 16-35/4L and the RF 14-35/4L, I would not say the latter is inferior. In the overlapping focal range, the optics are pretty similar. The barrel distortion of the two lenses at 16mm is about the same (3.5% or so). At wider than 16mm, the RF distortion is extreme, but the 16-35 doesn't go wider than 16mm at all. If you compare software-corrected images, the RF 14-35 is as good or better than the EF 16-35 across the range, and it goes to 14mm (or even 13.5mm if you use the right software). It's only 'worse' if you apply no correction to your images. Does that really matter? I'd argue that it does not. An argument can be made that without a lens correction profile it was inferior (mainly because the distortion is mustache-type, and that's hard to manually correct). Adobe was late in getting one out, but DPP had it from the beginning and DxO had one early on.
As for the 100/2.8 Macro, definitely agree that paying more for the RF lens with its design-imposed focus shift is bullshift. I'm keeping the EF version for sure.
The one you mentioned, the RF 70-200 has inferior construction/durability/resistance to ingress of contaminants (external focus design) as a trade-off for weight
I've not found extending zooms to be more susceptible to ingress of contaminants. I've seen plenty of dust in EF 70-200 lenses, and EF 24-70 lenses with none. I think the environment in which a lens is used is far more relevant for dust ingress than the sealing of sealed lenses. Canon has stated that the dust/water resistance of extending and non-extending zooms is similar (with the caveat that a front filter is needed for full sealing of some lens designs).
If I recall, zoom works in opposite direction and takes two complete twists to go from 70 to 200, which is slow and clumsy, and for what marginal optical improvement, it's not worth the extra cost, this is another where I'd rather keep my EF 70-200 f/2.8 III.
Sorry, your recollection needs work. The zoom rotation direction on the RF 70-200/2.8 is the same as all the other Canon zoom lenses. I suspect you're referring to the relative positions of the zoom and focus rings, which are reversed on the RF 70-200/2.8 compared to lenses like the 24-105, 24-70/2.8, 28-70/2, 14-35, etc. However, the relative positions are the same on the 70-200/2.8 and 100-500 (which for me is a little easier, since my white lenses both have the zoom ring further from the camera; it was harder with my EF pair, where the 70-200/2.8 and 70-300L had different positions).
The RF 70-200/2.8 takes ~90° of rotation (i.e. 1/4 the way around the lens), longer than the throw on the EF MkII/III but still easy to go from 70 to 200 with one quick hand motion.
As for the IQ, I was out shooting with a friend a few weeks ago and he compared his EF 70-200/2.8 II to my RF 70-200/2.8 on his R5. Hopefully he won't mind my sharing the results. There's a pretty clear winner and loser, and the improvement with the RF lens sure doesn't appear marginal to me.
Cost is certainly a good reason to stick with the EF 70-200/2.8 III, but I do think the RF lens is better in many ways (which is a challenge since the EF 70-200/2.8 II/III are excellent lenses).
I agree with your points on the other lenses. Also, with the RF 24-105L, I suspect that there is either huge variation, or it's grossly underrated. I've seen the charts, but some reviewers claim it's as sharp as the latest version of the EF 24-70 f/2.8L II USM, which was a sharp lens, while others say its just a bit sharper then the EF 24-105. I get stellar sharp images from mine, way sharper than from my EF 24-70 f/4, which was known to be shrper then the 24-105, so not sure what to believe. I'm curious what other people's experience has been with this one.
I've been quite pleased with the RF 24-105/4. I bought it with the EOS R, but I really didn't use it much since I had the 1D X and 24-70/2.8 II. Since getting the R3, the 24-105/4 has become my 'walk around' lens and I like the extra range. I don't feel that I've given up any IQ (although the 24-70/2.8 II was noticeably better than the EF 24-105/4 MkI and I had two copies of that). I also don't mind losing a stop of light since 1) one of the main reasons I went with the EF 24-70/2.8 II was for better AF, and that no longer applies with MILCs, and 2) if I want more light or subject isolation, I can go a stop better than the 24-70 with the 28-70/2).