One should be at the bottom one at the top. I understand space on the phone is a premium but a second port would make the phone so much more usable. Wired headphones, flash drives, camera modules, speaker modules, keyboards, even connection to a TV, all could be used while charging. It’s a shame it’s not a thing, USB is extremely versatile port, but you only get one and it’s used for charging half of the time. (I am aware dongles exist)
a) I have a USB-c headset at work
b) the 3.5mm headphone jack can’t be used to transfer data (at a good rate)
Not sure what exactly you mean by headset. But headphones and IEMs will use a 3.5mm or 1/4" jack. My sennheisers use it, my beyerdynamics use it, my audio Technicas use it. Even my KZ IEMs and moondrop IEMs use it. This is a universal standard for a reason.
And not sure what the data rate has to do with anything. It’s an audio connector, it’s not used to transfer data, it’s used to move the drivers in a set of headphones. As usb-c doesn’t output line level audio, any headset you have that uses it needs its own DAC and amp which is problematic for e-waste reasons.
Headset, as in headphones with a microphone. I use it for MS Teams meetings and a bit of music and it works fine.
The point OP was trying to make is that you can use USB-c for other things besides listening to music.
Since you seem to be an audiophile with a list of fancy headphones (don’t ask me, my Cardo combined with earplugs is fine for the level of listening I want to do) then wouldn’t an offboard DAC / amp that you could keep far longer than a phone, and isn’t restricted by size constraints going to be better than a built-in version?
Also, if you’re worried about e-waste maybe you shouldn’t buy so many headphones. My partner’s Sennheisers have lasted 20 years so far.