Right now, we have two pitchers one would consider "ace" caliber, at least at their time of acquisition.
One was traded for ad is living up to the hype and beyond. The other was acquired via free agency and, while pitching well at the moment, is only in year 3 of a 7 year deal and most of us are hoping and praying he accidentally opts out. It's easy to say now "If Ben had gone after Scherzer...". But it's not like Scherzer's future health and performance were known at the time, either. It's also easy to say now that Scherzer ould have been so much cheaper. Do you remember the market reaction after that deal was signed? It was far out of line from what was expected.
Really, look at all of the best pitchers the Sox have had in the last 20 years. Most of them were acquired via trade, which mitigated the length of their stay and probably the cost in many cases. This seems to always be the way to go. In fact, some times these pitchers are young enough to be extended and still mitigate the window of ineffectiveness at the end.
My biggest issue with Ben was his failure to trade away a few prospects. He could have acquired a few shorter term arms to sit a top this rotation had he been willing to do so, especially given how overvalued prospects were in trades at the time, especially A-ball prospects..