I tried, I really tried, to drop this conversation...but...
I think people hear your argument. They just don't find it convincing.
It rests on your definition of what the EOS-M system is and presumes that the EOS-M system can only ever be what you think it is.
My counter argument is that it's Canon's line of cameras and lenses and they can do anything they want with it.
Like you, my personal preference would be a 7DIII. But, I'm simply more willing to entertain the notion that it is at least a 50/50 proposition that Canon, if they ever again make a high-end sports/wildlife focused APS-C camera, will chose to keep the APS-C and Full Frame lines separate.
They never kept APS-C, APS-H, and FF separate in the EF system.
Why do people dismiss so easily the possibility that the difference between EOS-M and EOS R is something other than sensor size? It's like deja vu from 10-20 years ago when the only thing that mattered was megapixels.
You completely reject the notion that there is value in keeping the APS-C line and the full-frame line separate. I happen to think that there is at least some merit in such a decision and that there is at least a 50/50 chance that Canon may go that route.
No, I do not completely reject the notion. But there are plenty of voices here who argue that position, I see no need to repeat again what they continually post here.
I do think it is more likely than not the defining difference between the EOS M system and the EOS R system is not sensor sensor size. It seems to me far more likely, based on what Canon has done so far with both systems, the differences are about which types of buyers they want to attract with each system.
Much of your argument is also based on what lenses Canon currently makes for the RF mount. But, Canon can also make whatever lenses they want. If they decide to make a long telephoto lens in the M mount, they can do it. Having lenses in the RF mount doesn't preclude them from making lenses in other mounts. And, given the low prices for some of those new RF mount lenses, it doesn't seem like retail price would be a barrier to offering similar lenses in an M mount.
It's based on what Canon has done for two decades with APS-C, APS-H, and FF DSLR bodies and EF/EF-S lenses and what Canon has thus far done with both EOS M bodies/EF-M lenses as well as EOS R bodies /RF lenses.
Canon has had eight years to introduce EF-M lenses to the EOS-M system. If they wanted to sell premium EF-M lenses in the EOS-M system they have had more than ample time to introduce them.
Finally, I'm not even sure if Canon would make an APS-C R7 at a price point that would be reminiscent of the 7D series. The 7DII and the 5DIII came out before Canon changed it's sensor fabrication to on-chip ADC. With their more modern sensor fabrication, the cost of a full-frame sensor seems to have significantly dropped (based on the pricing of the EOS R and RP.) Could they make a feature-packed R7 at a price point significantly below the R5? Would they? Would they be better off putting those features into an M7 that sits at the top of the M lineup with no ceiling, instead of somewhere in the middle of the R lineup? Would that increase sales, because it would appeal to M buyers who want to own the best in the line, rather than R buyers who want a second body? Only Canon knows.
The EOS 5D Mark IV was the same price in 2016 that the EOS 5D Mark III was in 2012.
The EOS 90D was introduced at the same price in 2019 as the 80D in 2016 and the 70D in 2012.
Canon's pricing has always been market driven, not cost driven. Always.
The pricing of the EOS R and EOS RP were based on where Canon wanted to place them in terms of price points. Also, both sensors were retreads from the 5D Mark IV and 6D Mark II, respectively. That decision may have been based as much on how many they already had stockpiled on hand due to less than projected sales of the 5DIV and 6DII than on the cost of making them.
If Canon can't make a product at a desired price point they don't raise the price and keep the design, they change the design until it can be sold profitably at the desired price point.
But even if it were cost driven, if producing a FF sensor is cheaper post-2015 than pre-2016, then that would apply all the more to APS-C sensors. This argues against an R7 having to cost more relative to the R5 and R6 than the 7D and 7D Mark II cost compared to the 5D Mark III and 6D/6D Mark II.
The 7D and 7D Mark II sat squarely in the middle of the EF lineup. It was three times the cost of the entry level Rebels. It was one-third the cost of the 1-Series. Why do you think a mirrorless equivalent has to be "king" of its mount?
The typical M buyer outside North America and, to a lesser extent, Western Europe doesn't care about a ceiling. They are like most Rebel buyers a decade ago. They bought one and used it without worrying about the next Rebel coming down the pike. I've got friends still shooting with Rebel XTi and T3i bodies. I've got friends still shooting with Nikon D50 and D90 bodies. They all do tend to use their phone more than their cameras, though. But so do many EOS M owners. They only grab the camera when they're going to a special event like a birthday party or taking a trip, in much the same way that most other Rebel owners once did. The vocal Rebel users who wasted money (that could have been spent on lighting, better lenses, etc.) on every single upgrade that inhabit these forums are not the typical Rebel buyer.
Sure only Canon knows for sure what their current plans are. But history can be a pretty good indicator, especially for a company as conservative as Canon.
History is filled with generals and football coaches and baseball managers who were successful because they understood their opponents past history and tendencies better than their opponents understood theirs.
Clemson won the National Championship game in football in 2017 because their coaches did their homework about how lenient the Big12 crew calling the game had been all season long with letting offensive receiver throw picks. It caught Alabama off guard because neither SEC officials nor ACC officials had allowed the same thing.
One reason the Civil War lasted as long as it did was because Lee and the other Southern generals knew their northern counterparts, whom they had been instructed by at West Point and under whom they had fought the Mexican-American War, better than the Northern commanders knew themselves. The tide of the war only turned when Lincoln replaced his commanders with "unknown" generals like Grant, Sherman, and Custer who were as unpredictable to their foes as their foes were to them.