The 6 was a beautiful phone, and IMO their last good phone. It lasted me up until this year, and to be honest, my new Pixel is missing features that I love from OP, like the screen gestures for skipping songs.
I wouldn't trust them with another purchase again, though. I loved the 1 and 6, but never again.
It's basically an OPPO clone now. Oxygen OS is effectively ColorOS re-marketed. Unless you're chill with Chinese phones and software I would stay far far away.
Even back then OnePlus was sketch as hell. Remember their "ladies, take a pretty selfie and win an OnePlus" campaign?
I agree on the pixel comment. The pro is on the expensive side, but the 7a is most like the old OnePlus lineup imo. For 500 bucks or so you get a lot of phone. And the software is plain old android without much extra BS.