Generating set of a group and relation to diameter?
The answer to the first part of your question is yes.

Given a permutation group $G = \langle S \rangle$, there is a polynomial time algorithm (clearly more efficient than the brute force approach which has factorial complexity), the Schreier-Sims algorithm (https://en.wikipedia.org/wiki/Schreier%E2%80%93Sims_algorithm) which computes a base and strong generating set (BSGS) that can be used to compute the order of the group (hence decide if $G=S_n$).
A good reference seems to be Seress' Permutation Group Algorithms and especially chapter 4.

Also, this question can be solved in practice by using GAP $\texttt{IsSymmetricGroup}$ (https://www.gap-system.org/Manuals/doc/ref/chap43.html), which implements this method.