Real Linux on phones is a thing. They're usable, but most hardware is getting old. E.g. PinePhone still works fine, but they recently announced that it's unlikely that we see a new version. They mention that it's hard to be competitive with hardware when people can install PostmarketOS and SailfishOS on cheap old Android Devices for a similar experience.
Only if your threat model is equal to the one from the GrapheneOS crowd, and only if you value freedom less than maximal security. It's fine if this is your choice, just don't say this is the only reasonable choice.
Concerning "usable", Librem 5 is my daily driver. I have no backup phone.
Also, after skimming your link and seeing "Hardware kill switches are nothing but marketing frills", I can state that this is nothing else than FUD. Kill switches can protect me, when GrapheneOS can't. You have to trust that your proprietary modem never spies on you. I don't have to. Also, here is a couple of nice discussions of this article: https://news.ycombinator.com/item?id=37507414 and https://news.ycombinator.com/item?id=28500824
https://pine64.org/2026/03/24/march_2026_fosdem/#where-is-th...
In the long run - without PinePhone - people will lose more and more control over hardware and drivers.