I Believe The WM 14 Arc With Tyson & DX Was More Important For Austin/WWF Than WM13 with Bret.
As far as matches off the top of my head i believe that HBK/Flair match is up there the apex.
The Austin/HBK isn't even a 5 star match, much less as important as the two I mentioned. Austin winning the title was the a formality at that point, it was the match with Bret that validated him as biggest name in the industry.
And HBK/Flair isn't a 5 star match either and that match was only important to Flair and HBK's future storyline with Batista. You can argue that it set the tone for HBK's final run of his career because his last few WM matches mimic'ed his Flair match along with his retirement.
But as I said, that match only effected 2 people on a dramatic level. The Austin/Bret match completely changed what the WWE was about, set the tone for the ENTIRE Attitude Era and redefined what a face and a heel could be in the industry. There is not a single WWE match that is touching it.