I agree that overriding the value of `fill-column' _only_ inside doc strings is the sensible way to go. The only reason `emacs-lisp-docstring-fill-column' exists in the first place is to cover the edge case of doc strings as recommended in https://www.gnu.org/software/emacs/manual/html_node/elisp/Documentation-Tips.html (e.g. for apropos) which is fine, but overriding it in any other situation is confusing. We already have a general mechanism for controlling the fill column width on a major-mode basis through hooks and `fill-column' being buffer-local, and should as a rule encourage the use of these consistent control mechanisms across all major-modes - not introduce redundant functionalities that fight each other.

The proposed solution in this email thread by Noam Postavsky is already too greedy in that it affects _all_ strings, not only doc strings (or maybe I misunderstood "(nth 3 (syntax-ppss))" ?). Still, it's better than the current behavior, and I guess that identifying doc strings only (and not strings in general) is too difficult.