I wonder if there are any viable alternatives though.
For the future, Graphene OS devs have stated publicly that they're working with an unnamed hardware vendor to develop a phone that will meet their list of hardware requirements. Currently only the Pixel line does. From what I understand, a few Samsung phones come close, but don't support bootloader re-locking... When you unlock Samsung bootloaders it burns out a fuse on the board which in turn completely disables Knox, their architecture for a trusted execution environment.
My perspective is that I want one or two devices in my life, ideally one phone and then either a tablet or small laptop, which are maximally secure and almost never leave my direct custody. I am willing to give up root on these devices to achieve that level of security. Though I'll note that sideloading apps is absolutely possible on Graphene OS.
There are plenty of other general purpose computers at home on which I have root access and can use to tinker and experiment to my heart's content, and which I do not use for highly sensitive personal information (banking, primary email, etc).
The other important difference for me is that, whereas Graphene OS restricts root access for end-user security, companies making locked down devices withhold root from the end-user in order to keep control for themselves.