I'm not sure as others why others feel this is a major change.
OnePlus was always a subsidiary by Carl Pei [1] who eventually left the brand to create a new gadgets/tech company.
Nothing [2] is the next project he started that keeps many of the ideas started with OnePlus, good value for money and aim for quality Android.
Bootloader also seems to allow unlocking [3]
In recent years OnePlus was just another Chinese phone.
But if I've misunderstood something, I'll appreciate me being corrected.
[1] https://en.wikipedia.org/wiki/Carl_Pei
[3] https://nothing.community/d/6047-policies-for-rootingunlocki...