But... are they selling? I have no idea about sales data. But Canon's aim is to sell RF lenses (agreed) and how many of those 2 exotics will they be selling if there is no improvement vs the EF ones apart for the need of the adapter? And then there are some small disadvantages as well. But everything pales in front of the cost differential.
Current market price for a new EF 400mm f/2.8 L IS III - $11,999 USD. (If you can still find one from a retailer you trust)
Current market price for a new RF 400mm f/2.8 L IS - $11,999 USD.
Current market price for a new EF 600mm f/4 L IS III - $12,999 USD.
Current market price for a new RF 600mm f/4 L IS - $12,999 USD.
Yeah, that cost differential is just ridiculous, isn't it?
For most of the time since the early 1990s, which is when Canon passed Nikon to be the preferred system among professionals shooting the 135 format, the overwhelming majority of purchasers of Super Telephoto lenses have been photojournalists, sports shooters, and wildlife shooters - all of whom made a living with their work. The advantages of putting USM AF motors in the lens, rather than using mechanical linkages to a more conventional motor in the camera body, is what precipitated this sea change. In the late 1980s at the beginning of the AF era, Nikon held over 80% of the professional market in the 135 format. Canon was a distant 2nd, then a multitude of other players trailed them. These were companies such as Leica, which had been steadily losing share to Nikon since the 1950s, Minolta, Pentax, Konica, etc.
Very few of those PJs, sports specialists, and wildlife professionals tended to update their Super Telephoto lenses every time a new version was released. The ones from the 1990s were more than good enough for newsprint, magazines, and web based images. They only tended to buy the newer ones when the old ones could no longer be repaired. [I've got a friend who is the entire photo department for a mid-market local newspaper owned by Gannet in a town with major college athletic programs that up to a year or two ago was shooting major college football, baseball, soccer, etc. with a 1999 vintage EF 400mm f/2.8 L IS mounted to a 2012 1D X Mark II and a 70-200/2.8 on a 1D X.]
Unlike more mass produced camera bodies for consumers, newly introduced Super Telephoto lenses did not tend to sell most of their units in the first weeks or months after introduction, drop sharply once all initial orders had been filled, and then gradually fall off until the next model replaces them. It tended to be steadier over the entire time the lens was in the catalog. If an updated lens is cheaper per unit to produce, changing production over to the newer model helps to defray the cost of R&D needed to get that lens to production. If there's little or no change in the optical formula, then the R&D cost is already reduced to begin with.
This may have changed to a degree with the massive reduction in the numbers of full time photojournalists and sports shooters working for newspapers, magazines, or agencies that issued company owned equipment to their photographers in the most recent decade. As the top end of the market for exotic telephoto lenses has shifted to amateurs and hobbyists with large disposable incomes, it may be the case that there's more of an initial surge now than in the past.
Since the EF versions are, for the most part, no longer available new (or won't be when existing stocks dry up) anyone needing to replace an EF Super Telephoto lens who wants to stay with Canon will have no choice but to use an RF Super Telephoto at whatever price Canon and their retailers are charging (Hint: for the 600/4 and 400/2.8, the prices are
exactly the same, respectively, for the EF III versions and the RF versions of each). If they're not already using Canon EOS R bodies, then they'll also need to buy some of those, too.
