OBP and SLG were the two offensive stats most highly correlated with runs scored. But at the time people were more interested in AVG and RBI, while guys with high OBP were undervalued. OBP is most definitely a more valuable stat than AVG as AVG ignores the value of a walk in terms of avoiding outs. And SLG is better than RBI because RBI are heavily team-dependent stats (hard to get RBI without men on base). And OPS (the combination of OBP and SLG) is a decent combination of the two. I don't think they said OBP is three times more valuable than SLG. If anything, I can see an adjustment made to put OBP and SLG on the same scale (since SLG can go up to 4.000 while OBP can only reach 1.000).
As for pitching, I don't think Moneyball professed that the only thing that mattered was K, BB, and HR allowed. They just said that these are the only stats that are solely a function of the pitcher. Everything else (hits, runs, earned runs, etc) are team-dependent in that they rely on the abilities of the defense behind the pitcher as well as the pitcher. And this is most certainly true. But I think the more interesting thing about Moneyball with respect to pitching was that they were the first to start the understanding that wins (and to a lesser degree ERA) were being highly overvalued (because wins were dependent on the team's defense, offense, AND bullpen as well as the actual pitcher).
But the simple answer to your question is: yes. Moneyball was dead on when it came to SABRmetrics. And the proof is in the pudding. Nearly every team in baseball has since hired statisticians to their front offices to help make smarter baseball decisions. And teams like the Red Sox and Yankees have used Moneyball principles (combined with huge budgets) to dominate the regular season for the past decade. Similarly, teams like the Rays have survived thanks to a similar approach to baseball thinking. And while the Cardinals may or may not explicitly be following Moneyball principles, their key players (Pujols, Edmonds/Berkman, Holliday, Carpenter) very much embodied what Moneyball was all about.
The irony is that, in agreeing to be the subject of Michael Lewis' book, Beane arguably torpedoed his team's chances to remain competitive. Now that other teams are using similar statistically-minded approaches to baseball decision making the Athletics and their small budgets are finding it hard to compete again.