I have owned / used the OnePlusOne, OP2, OP3T, OPX. I have also owned Nexus 4, Nexus 5, Moto G4 Play.
This last week I put LineageOS 15.1 on my MG4P and on a 2013 Nexus 7. Because I can.
In total across everything I have a 2016 Moto G4 Play with LineagOS 15.1, OnePlus 3T with stock, Nexus 7 2013 with 8.1, Lenovo Tab 4 8 Plus, Nexus 10 on Pure Nexus 7.1.1, Google Pixel C on 8.1, Chromebook, and Windows 10 laptop. And some Raspberry Pi clones on Debian.
I am conflicted. I can spend a day with a $99 2016 Moto G4 Play and it works well enough. So you can be OK with older cheaper tech. I have a 4 year old 7" tablet with current shipping Android and it works quite well too.
I have cracked open and repaired Nexus 7 and Nexus 10 and got a decent 4 years life.
The biggest problem I have with the newer OnePlus is the creeping increasing price. I am not clear the extra money does actually make a sufficiently better product. What I think is happening is OnePlus copying Apple's hype bubble of milking a brand.