It all depends on your personal definitions of 'shiny' and 'work' I suppose. Current GNU/Linux phones unfortunately don’t even clear the ‘work’ threshold for me, and are far from it.
If current GNU/Linux phones work for your needs, that’s great - but sorry to say that you are not representative of all users (neither am I - that's the point, kind of - Android/iOS are mature enough to cover most users' needs). I don’t want to go into too much detail of my specific needs, but let’s just say the deficiencies boil down to (a) vastly inferior power management/battery life, (b) vastly inferior processing power in the current crop of hardware and (c) specific apps/services not being available on the platform (and likely impossible to run via Anbox because of (b)).
I would actually love to jump to a GNU/Linux phone. Less so because of freedom or privacy concerns (they are a factor, but not the dominating factor). More because I prefer the traditional desktop/general-purpose-computing OS way of doing things (file-centric vs app-centric, root access to the entire file system, development directly on the device). I would honestly be fairly happy with Android if it was pre-rooted, imposed fewer restrictions on what apps can do, and was based on a mainline kernel ideally.
I have previously used Ubuntu Touch for about a year on a secondary device, I have a Librem 5 on pre-order, and I follow development for the Pinephone somewhat closely and am tempted to get one. But for the foreseeable future I can't see a GNU/Linux smartphone replacing my Android - I'd see it as a complement to it (a tiny portable laptop).
Linux on the desktop is eminently usable, and many people do use it daily to get work done. I have yet to see someone make something usable for mobile.
MMS doesn't work on any FOSS non-Android Linux phone I'm aware of, so they definitely do not work for a significant percentage of the population even for basic group text messages.
Building an alternative phone OS is much harder than building an alternative desktop OS—the requirements are much higher (battery life, cellular, app support) and the mobile web is far less developed as a stopgap compared to the desktop web.
Desktop Linux is usable for most developers and people who don't care about UI consistency or proprietary applications like Office and Creative Cloud. That's a reasonably significant chunk of the computer-using population. The same cannot be said of phones.
No, that's just a technology that I consider "basic"—and one which most Americans use at least a little, even if the experience is terrible. And it does work for most people, even if it compresses images to oblivion and is slow to send messages.
My bar for widespread adoption is far higher, but it may be somewhat unattainable and it's definitely not necessary for the types of people who use desktop Linux. Even if you're happy with desktop Linux—in other words, your expectations of integration and proprietary software support are low—you won't be happy with current Linux phones.
On the Linux phone I have (pinephone) with the carrier I have (At&t) there is a script that can pull and send mms messages. There's work to get this integrated into libpurple sms so it you can use it from a shiny GTK3 app just like sms.
I think it would be good to point out that MMS often doesn't even work on android phones. So making that a requirement is a bit silly.
It's not shiny but it does work. Continuing to use abusive software is a disservice to yourself and everyone around you.