It now becomes either something I have to carry around with me always; or buy one for each 3.5mm headset I've stashed.
Add the poor reliability and performance, and we come back to your point:
"Yes we shouldn't have to, yes it's a step backwards, yes it's not as good"
Exactly. So I will absolutely do whatever I can to make my life easier - but I also refuse to pretend this does not make my life needlessly harder - once again, for no obvious gain for those who defend the decision.
Phone jack is inherently different than all the Firewire/Zip drive items. There are literally thousands of technologies, interfaces and standards that live and die like fireflies. But the phone jack is a century old and still works perfectly well, and we have replaced it WITH the technology of the day - who thinks their $300 Bluetooth Bose will work 20 years from now? Or seemlessly plug in to each device they use?
"I've now spent several hundred dollars on the best-reviewed, bluetooth headset for my conference calls, and it's nowhere near as good, or convenient, as my $29.99 wired headsets"
You could buy 50 3.5mm+lightning dongles for several hundred dollars, and stick them on the end of each headset, which sounds more convenient than messing around with bluetooth.
I was thinking of the terrible headsets that some collegues use -- they have USB-A plugs on the end, for laptops. Not sure what they do if they want to join a call from their phone (say out walking). My 3.5mm tip+ring+ring+sheild headphones works on laptops and phones, seems far superior to their single-use devices. But western economy is built around selling you something new every 2-4 years, so needs obsoleting.
Yes we shouldn't have to, yes it's a step backwards, yes it's not as good, but I suspect it would save you a lot of problems.
Don't let perfect (a phone company making a phone with a standard cabled audio interface) be the enemy of good (a solution for your problem).