A lot of factors to consider. Williams played in a very good hitters ballpark. Ruth played in the all-time hitter’s era. Ruth didn’t have to deal with night baseball, sliders, a pool of pitching talent that just happened to have a greater concentration of melanin in their skin. I agree (and thereby amend my ‘not even close’ pronouncement’) that Williams was close.
Ruth played the middle and late portions of his career in high-offense era, but values such as OPS+ and wRC+ are adjusted versus the league average. Ruth leads all-time in OPS+ with a 206 value versus 190 for Williams).
As for the introduction of non-white players, it wouldn't have made much of a difference in Ruth's case. He hit Negro League pitchers even harder than the white MLB pitchers (source: Bill Jenkinson). In addition, check out the stats of Stan Musial and Ted Williams (the only hitters comparable to Ruth whose careers straddled the integration of MLB starting in 1947). They were almost exactly as successful after integration as they were when MLB was all-white, and the integrated portion of their careers included their age-related decline phase.