If you move to using an unsecured “chinaphone” as an alternative to the big three handset vendors, then it’s unlikely they are target devices for the myriad of uncertified ROM’s.

Not following your logic here… With the mainstream devices now locked, “the myriad of uncertified ROMs” will necessarily shift to the remaining unlocked phones, or die out.

I think a viable future is owning two devices, one “certified” to access your banking and work apps, and one running GrapheneOS for your private life.