>> > why is ((lambda...)...) deprecated?

Is it because of this kind of inconsistency?

(funcall (lambda () (message "hi")))         ; Prints "hi"
(funcall (progn (lambda () (message "hi")))) ; Prints "hi"

((lambda () (message "hi")))                 ; Prints "hi"
((progn (lambda () (message "hi"))))         ; Lisp error:
(invalid-function (progn (lambda nil (message "hi"))))

One would hope either that the last two both work or both not work.