I would argue the value add of the Pixel 6 is the proprietary Google SW. I was considering the Pixel 6 only for its photo abilities, and a lot of those are via Google SW - not fantastic lenses/processors. If I replace it with a custom ROM, the OnePlus is probably a better device (faster processor, etc).
If the Google SW is so buggy, there's no compelling reason to buy one just because of the HW.
Would I get access to the proprietary camera features with these? If not, what's the point of getting a Pixel 6 and putting a custom ROM on it when there is better HW out there?
I lost my confidence in OnePlus when one of their OTA updates soft-bricked my OnePlus 5 on Christmas Eve. Lost all of the data that wasn't backed up, since I had to perform a complete wipe and the phone was encrypted.
Have you considered OnePlus? Their cameras aren't the best, but they're usually as good as the other top brands in everything else.