So. Let’s have it.
As I referenced in previous post, we grant various rights to humans who by any reasonable metric have less sentience and control to adapt their environment to them, than do to various individual animals (as others have enumerated). So clearly we grant certain rights to our species as a class (with certain exceptions to be sure) mostly independent of individual sentience barring at the extremes.
Yet we are pretty stingy with rights for non-human sentients. Oh pets get protections. The cuter and more anthropomorphicable ones more of course. But that’s based on our feelings for them, not any measure or proxy of sentience or intelligence.
It seems that we are speciesists more than sentientists.
I would guess that any move to consider “humanzees” a protected class with internationally agreed rights and protections from abuse and from being taken advantage of would be more driven in the public sphere by their physical and genetic similarity to us than by their behavioral (next though) or intellectual (last) commonalities.
That seems wrong. Sentience that is within a different physical form and of a different sort than ours should be granted rights as well. But that is not how human psychology works. We have enough problems granting full rights and protections to other full fledged humans who look or behave differently than our own individual groups.
Humanzees would get some protections but not too many.