So, bad news. I started with the OnePlus3T. The display was... moderately unusable out of box with OxygenOS.
After a couple hours of flashing, I got Paranoid Android onto it - and immediately noticed a couple things.
First - and most importantly - the display was better but not great. I will play with it a little, but I'm not hopeful here. Whatever made it usable for the other folks on here who found it to be ok... clearly doesn't do it for me.
Secondly, I had a similar problem to AGI, where the WiFi didn't work and some other ancillary things (screen unlock, etc.) were a little goofy. I'm confident I can overcome these issues, but only if the display is worthwhile.
I'm going to restore to the latest OxygenOS, and take it from here.