As someone "upgrading" from the OnePlus 3:

It isn't about the hardware, and it also isn't about PureOS itself. It's about people caring enough to build an entirely new mobile operating system which actually respects your privacy and gives you tools to ensure it.

I'm really amazed at what they got running in the few years this project existed. Of course the phone won't be some spectacular mobile gaming machine, but that's not what I paid for. I paid for a privacy-respecting, secure phone. I paid for getting Linux to run on mobile OSes. That's what is important to me and many others.