I don't think anyone ever really thought a BB was the same as a single. From a strictly run expectancy standpoint, a single has always been worth more than a BB on the whole. The value may be roughly the same with no one on base, but overall... a single has always been worth a BB.
The whole Beane thing was that baseball in the early part of the century didn't properly value BBs relative to singles. That the market would pay $1.00 for a single, and $.50 for a walk when a BB is much closer to a buck than 50 cents.
It was about exploring walks being undervalued relative to singles, not that BBs were better than singles.
Well, with no one on base, isn't the value exactly the same?
I think some of that first wave of analytics revealed, perhaps obviously, that the worst thing you can do when you are hitting is make an out. And to avoid an out, however you do it, even with a BB, is the most important thing. That is, the thing that has the biggest effect on the probability of scoring in an inning, next to a home run of course, is making an out. So, don't make an out. "Keep the line moving."
But of course, with men on base, a single is more valuable.
I have a busy day so can't look up right now, but wonder how a BB and a single are calculated differently in RC/27 ...