These are all really important questions, and its great that you want to engage in discussion about it!
Have you looked at the Moral Weight Project? It’s a great piece of work that tries to tackle the (very complex, as you state) issue of comparing the welfare of different species, including humans. All their assumptions are explicitly listed, so you can look through and see where you disagree. There is a great sequence about it on the forum here: https://forum.effectivealtruism.org/s/y5n47MfgrKvTLE3pw
And I also wrote a couple of more accessible explainers of the project here:
These are all really important questions, and its great that you want to engage in discussion about it!
Have you looked at the Moral Weight Project? It’s a great piece of work that tries to tackle the (very complex, as you state) issue of comparing the welfare of different species, including humans. All their assumptions are explicitly listed, so you can look through and see where you disagree. There is a great sequence about it on the forum here: https://forum.effectivealtruism.org/s/y5n47MfgrKvTLE3pw
And I also wrote a couple of more accessible explainers of the project here:
https://docs.google.com/document/d/16EdSGP1-xs0Mh4G6QfQYOaaYfduDEpp32NK5BBlznYE/edit?tab=t.0
https://docs.google.com/document/d/1SIurNLZB8hSXTCKUNmREHmBt2sP4IQ4R0XkdYAZbYp0/edit?tab=t.0