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)
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.