With all the respect, to deny the progress we had in the last decade seems a bit stubbornish and counterproductive.
In the 2000s, uo to early 2010s, not even a basic non techy user could properly use linux without assistance, and nowadays, they can use it normally. Most of them just need a working browser and a good UI.
I don't say that out of nowhere. I've been doing some work in initiatives for digital inclusion in my country, and we're having great results with linux nowadays, while it was impossible some years ago.
There's still a lot that needs improvement, but we're nowhere near the state we were just one decade ago.
I understand your bad experience with GSIs, but I think it's a step in the right direction. The way custom roms have been made through the years isn't sustainable for the long run. It's too much work for the few people involved, that goes obsolete so fast. But with GSis, the projects will one day be able to maintain just a few images, and the porting community will just have to focus on unlocking the devices.
GSIs aren't working 100% today, but it's something still new in the perspective of manufacturers, and the tendency is to have better support with time.
Just to put things into perspective, my experience, as someone poor from a third word country, is just the opposite. In the past, only the more expensive phones had custom rom support, and the cheaper ones I got access to, wouldn't even get results if I searched for the model on xda. Nowadays, even cheap chinese phones or the ones locally manufactured in here allow me to put a GSI and have a customized experience, up to date with security patches.