I think your personal situation with your mom clouds your judgement. I don't have alopecia, don't know anyone close to me with alopecia, and didn't know Jada Pinkett Smith had alopecia when I saw the "slap clip" the first time. I don't really follow Will or Jada Pinkett Smith's careers. I like both actor and actress. I knew she had an affair and it was public, but never saw any of their podcast or interviews about it, because I just don't care about celebrities that much. I know the Smiths are rich, famous and good looking. Jada Pinkett Smith very much so.
All the above is framing for what I say next.
I heard Chris Rock's joke and after the slap thought the same thing as he said: "It was a GI Jane joke." Not just that, Jada Pinkett looks gorgeous with her shaved head, just like Demi Moore looked gorgeous with her shaved head. Both women are beautiful, so "the joke" (in my mind) came off to me as a suck-up compliment, not a comment on alopecia.
Why is everyone expected to know about Jada Pinkett Smith's medical condition? That is ridiculous. Does ANYONE, EVER get upset about comedians making fun of bald men? No. Male pattern baldness is a medical condition as well.
Will Smith was wrong from start to finish for all the reasons you stated, but Chris Rock was fine. Rock stated later he didn't know about Jada's alopecia. I take him at his word.