"I think you're missing the points here."
I think I'm entirely understanding the points you're making, I just think they're meaningless or useless. For example:
"1. It's already won, on sheer numbers, or by unit sales, or by value of sales, or by number of users, or by almost any other metric you can suggest."
Except the metrics I mentioned above, the ones I actually care about: system openness, user choice, and hardware and software longevity. All of your things really do boil down to "number of kernel installs on [some market segment]". I don't care about that. You clearly do, but that just demonstrates that we have differing goals.
"2. [...] The desktop is one battle in a war, which is arguably for user eyeballs, or bums on seats."
As I see that war, Linux is losing it. Linux may be beneath Android, but nobody says "I'm running a Linux phone". They say they're running Android, and that's what they have. Linux does not get user attention, doesn't convince the average user to do anything, and matters little to them. If their phone switched to Android on Fuchsia but looked the same, they wouldn't care. If it switched to any mobile Linux, they would be incensed.
"3. The real success story is FOSS over proprietary software."
Chrome OS and Android do not prove that. Large chunks are proprietary, the open chunks are frequently violating the spirit and sometimes the letter of the GPL, bootloaders are often closed source and locked down. But it is Linux, so we can call the entire thing FOSS when it doesn't bring much of the freedom or openness.