Yes, I agree, there are certainly other aspects.
A good SEO will know of all the aspects that website tries to achieve and will make sure that the SERPs performance is not compromised by HOW these other aspects are implemented.
What I am trying to say is that a good SEO does not need to know how to design the site for better accessibility, i.e. they do not need to be accessibility expert. What SEO job is is to ensure that the choice of accessibility implementation does not compromise the site in SERPs.
So ideally the end result (accessibility) for the user is the same, but the technical implementation may differ from the choice that may have been made if SEO consultant was not involved.
I think "SEO" is unfortunate term as it is often connected with manipulation. Today's SEO has expanded on what it covers, also because of the usage signals, but ultimately the task is still Search Engine Optimisation.