Upgraded to Pie this morning. Just read some comments on Reddit that the Bluetooth problems that had plagued OnePlus since Oreo, have been sorted! Worth a try! ;)
I have a 5t and it has no problem whatsoever with wifi.
The bluetooth problem can be ameliorated by changing the AVRCP setting in Developer Options. I initially has the same problem you describe but it was an easy fix.
My phone is almost a year old and is still lightning fast, in fact the...