What you say is mostly true expect you don't get that Rec.709 means many possible gammas and this is the root of all problems.
For OSX Rec.709 (1-1-1, which you always get from YT) means about 1.95 gamma. You never use this in Resolve (you will use sRGB, 2.2, 2.4).
You can/should grade to standard gamma, but if you want good YT preview on OSX you need to export special version with Rec.709-A as gamma. Of course this will look bad on PC which doesn’t expect 1.95 gamma but sRGB or 2.2 or 2.4 depending on the player/browser.
We’ve been over this countless times and nothing changed. Maybe one change is that reasons are known now and confirmed by different companies/people.
There is no real solution atm.
Best solution is an introduction of standard tag for BT.1886 which then could be respected by all parties in the chain, but this requires actions at top level - ITU etc. They failed to introduce one (when BT.1886 was announced). They done it for HDR and this is fine. At least you can tag file as PQ or HLG and there is no problems with it. Imagine single HDR tag which could mean both HLG or PQ- how messy would that be
Another solution is for YT/Vimeo to accept and properly pass sRGB grades (now they will change tag to 1-1-1)- this works fine on Mac and it would work okish on PC as well. I've tried with Vimeo- they acknowledged it, but done nothing more.
What you say is a lot of general principles, but this is not how current reality works
You still have not answered my question, just keep repeating same "theoretical rules".