You're saying nobody can become proficient (not "deeply conversant") in lisp in 3 months because I can't become deeply conversant in lambda calculus in 3 months?!

nobody, proficient, lisp. I, deeply conversant, lambda calculus. You're comparing apples and oranges.

I learned lisp (pretty deeply, I'd qualify myself as intermediate then and now) in what... 5 or 6 months? And I was alone. And I didn't know emacs. With some coaching and pointers I'm pretty sure I could have made it in 4. Aren't you happy?

Well, we have 2 data points now. I guess we can agree that it's harder to learn than Python :-)

For what it's worth, I think learning Lisp is useful for getting (re)acquainted with lambda calculus if nothing else.

lisp doesn't strike me as a difficult-to-learn language. it actually seems the easiest of them all, definitely not harder than python to pick up. c++ is at the other end