Yes, and that combo would cost over €12k, while an original 200-600mm f/5.6 would probably cost a third of that. Plus, there’s no guarantee that its image quality would be as good as a native 200-600mm. A 2x teleconverter is very taxing on image quality.
I guess it really depends on your priorities. Even amongst enthusiasts, most people simply don’t have 5 figures to throw away on big whites. And of the ones who do have the money, many simply can’t justify the expense regardless. I think many are willing to accept some “caveats” if it means getting a 95mm aperture telephoto lens for a fraction of the cost of the >100mm options.
If they surprised everyone and made the max magnification 0.5X I think it would shock everyone (well, who's into that) if they saw the high magnification at-distance photos with background blur it would allow. For some (well, me) that would be an enormous reason to get it - as I'm into that as much as using it with normal and long distances. However, I doubt (strongly) that Canon would do this. As for price, I see this coming in around $3999 in the US. I have the 100-500L and the difference to get this probably isn't worth it to me. But I do think it would sell well at that price with people (like me) who don't want to use a TC (and thus wouldn't get the 100-300 f/2.8 & 2X TC) and don't have the 100-500L.
I suspect 1:2 would cause massive focus breathing or cause the lens to be much longer in size.
I live in the USA and I did rent a 400mm f/2.8 back in Sept and I loved it, but I don't think I would ever buy one. It's pretty cumbersome, but it did force me to be tripod guy again for a while, which I kind of liked.
The 400mm f/2.8 was definitely a step up from the 100-500 7.1 and 200-800mm f/9 that I normally use. The photos were easier to handle in post and I got better results. But with the newer mirrorless cameras, and the newer denoise software and now with Adobe adding lens blur etc, I don't think its worth the extra weight and size, not to mention cost for the big white lens. For certain results were better, but it's not as much in 2024 as it was say in 2018. Not nearly as much of an advantage as it used to be.
No way, RF 100-500 is an extensive zoom (horrible for beach scenes like surfing) and not 5.6.
A 3.5kg 200-800mm the ultimate bird in flight lens? OK for an Olympic weightlifter with lightning reflexes but I couldn't hand hold it to move it rapidly for fast erratic BIF at 800mm (or less).
The 400/5.6 is a very good lens. Worth noting that 400/5.6 is effectively the same as 500/7.1 in terms of light gathering, and also worth noting that prime lenses collect dust, too (according to Uncle Rog / LensRentals, the worst offenders for dust/debris in the lens are primes, not extending zooms).
Also if you want a now relatively cheap alternative to the 400/5.6, the 100-400mm II superseded the 400/5.6 in just about every way, being sharper according to Uncle Rog and Canon's own charts (as well as my direct experience), and having the versatility of a close-focussing zoom with very good IS.
Got your point, but my experience is that my Canon EF 400mm 5.6 L using +12 years for surfing has the same dust inside that my Canon RF 70-200 f4 L (extending zoom) collected on beach 2 years using much less.
I believe what you wrote but:
Yes, the EF 100-400 L II is an excellent lens. I kept that and added the RF 200-800 as well as the RF 100-400 (for portability). Have not sprung for the RF 100-500 and at this point see no reason to. Love the 200-800 as it is perfect for handheld hummingbird work.
