Features removed

USB protection — the low-level USB port controls rely on Pixel-specific hardware and are non-functional on other devices

they don't need to outright remove that. I know that at least some fairphone models are capable of that, because another ROM makes use of it. it seems it was more important to have a much broader compatibility quickly, without testing what features do really need to be removed for what devices. there are probably other removed features too where tbis applies

but this is not all that graphene gives, I believe this does not make it worthless. they have other unique features too like sandboxed google play and the possibility to manage sensor access for apps separately, and more.