Yeah you are probably right, Google could at any point (for example) lock the bootloaders on Pixels, which would mean no one could install GrapheneOS in the first place.

They are still kneecapped in the sense that they are still developing on top of AOSP, so sadly the bi-yearly code drops will probably still affect them greatly.

No getting around that though and there's always the possibility Google restrict access to AOSP source code to the point where GOS can no longer access it, in which case the sales of their new phones might allow them to go down the road of full development of their own hard fork of android from the last released version (that might be an impossible ask, I dont know).

Anyways I'm specticilatin' 'ere