Some headline apertures ratios are narrower* on RF lenses than what came before, but again this issue has been blown out of proportion by forum chatter. The best example is the RF 100-500, which is no narrower than the EF 100-400 which it replaced, it just adds more focal length and so the maximum aperture at the long end is a narrower f-stop. The only objective deficiency of that newer lens is the weird extender compatibility restriction.
The extender approach for the RF lenses has been a bummer for me. I'm also still a fan of always-on manual focus with the AF in perpetual servo when I'm in the countryside, and between the two my EF lenses continue to dominate my trips. The sharpness and faster AF simply haven't been sufficient game changers for me to outweigh the loss of functionality for the (incidentally) mechanical focus capability and extender compatibility. Given Canon's subtle movement back to equivalent capabilities I think that they're well aware, but have simply sought to solve other complaints first. AF is fast and amazing, but not perfect and susceptible to poor choices when branches and long grass become involved. Canon will get there with the 3rd or 4th generation RF lenses, no doubt.
*Better high ISO capabilities is one reason for this, as you say, but as has been discussed on these forums in the past, (probably) the main reason Canon brought out RF lenses with narrower maximum apertures is that the mirrorless system allows autofocus in much dimmer light, so they were no longer arbitrarily restricted to f/5.6. I'm sure we would have seen such lenses in the EF era otherwise - it's not a drift towards darkness, it's an opening up of more possibilities in lens design.
I'll be pedantic, but I feel that given contrast focus was available long before the R showed up it's actually the EVF that made this broadly reasonable. I do like my EVF! But I hear your point.
I don't know if any camera release is ever done as a thank you to existing customers. They just want to sell as many as possible - to whomever they deem most likely to part with some money.
I've founded a few successful companies, and have lead significant segments of (continue to lead) a few large ones. I think that both can be true. But why I worded my claim this way:
Prior to the R, the primary general purpose 35mm DSLRs for Canon were the 5D and 6D series, right? The 5D was configured in a way that it best assured things got done for people who needed to do it—whatever that was—and priced it accordingly. The 6D was configured to be technically eligible: For a much lower price, one got a 35mm sensor with OK light sensitivity, half the shutter ceiling, and passable weather sealing. Thus it was in one shade or another for years. The X0D series was actually competitive unless you had to have the 35mm.
Eventually the R came out as Canon faffed about figuring out what it wanted to be in the mirrorless world. But nothing to really change the status quo for the average Joe or Jane.
Then Canon releases the R5 and R6—the R5 was clearly spec'd as the camera that gets it done for general cases for those who need to do it—and priced accordingly... but the R6? Canon lifts the sensor and much of the tech out of the then-flagship 1D series and drops it in, matches the shutter to the R5, doubles the ISO of the R5, smokes the DR, and puts in real (for the time) moisture/dust sealing. And
then for whatever reason while the R existed sells it for a fraction of the cost of the R5 and within inflation reach of the 6D II. There was no need to do any of that -- the 6D series had set the pace, and people were already buying it; ditto for the RP. In the Canon context, this combo made performant camera capabilities at the 35mm level a reasonable stretch for the prosumer -- the pain from lesser capabilities really didn't apply to most people. Naturally it became Canon's best seller, probably because people doing non-paid camera things are more populous than people who get paid to do camera things. And this spoke to them.
Yes, Canon was wise to take this approach to sell more cameras. But yes, they also went above and beyond for people who'd like this kind of device but don't need this kind of device as a general statement. It really, in my mind, came off as a generous thank you (love letter?) for all those who didn't jump ship at the 6D tier, or came quickly back, while Canon lagged in the mirrorless arena.
Of course, all of this is known to the forum here -- but it bears repeating when the term "love letter" gets used and we're debating "what next for the R6 series" in the context of prosumers. I totally agree with the earlier remarks about the VCM and hybrid videos being an essential for modern sales and interests (just thinking of my own kid...) but the move with the paper specs for the R6 III also feels more 6D-ish and less R6-ish in the I and II contexts.
I want the 2015 R6 spirit to live on in 2025. Whether or not I stick with the R6 is immaterial, this is what I want Canon to be known for. Not the 6D.