Now to be fair, Williams was hurt in the 46 Series. Hard to believe now, but there was a full week between the end of the regular season and the first game of the World Series. The Sox played a some exhibition games against a group of all-stars to stay sharp, but Williams was hit on the elbow in one of them and had it swell up on him to the point where he couldn't swing a bat for several days. He "healed" in time to play, but all indications are he was not anywhere near 100% and unfortunately, it was his only shot.
Ortiz has had the advantage of multiple postseason series and years to cement his legacy. We remember the fantastic fantastic series and tend to overlook the not so good ones: 2-21 against the A's in the ALDS in 03. 4-17 against the Angels in the 08 ALDS followed by a 4-26 against the Rays in the ALCS. 1-12 against the Angels in 09. 2-22 against the Tigers in 13 (1 of the 2 was a pretty big hit as I recall).
Make no mistake about it, Ortiz has been the man many times in the postseason. But he also has had 75 more postseason games to build that legacy.