A study a few years ago suggested that if we wanted to approximate true offensive value (minus baserunning of course) with OPS a more accurate formula would be: 1.4*OBP + 1.0*SLG.
Saying OPS already counts singles twice really does not mean much since the biggest value of OBP is not making outs. 2 singles and zero outs are worth more than 1 double and 1 out.
Also, looking purely at Crawford's small sample in AAA is not really a definitive conclusion on whether he is ready. I think he puts up a 700 OPS in the majors from day 1 if he was recalled and the higher OBP makes him more valuable than Galvis. His projections are slightly below that but not too far. On Fangraphs his three projections are: 678, 666, and 689 and I think those build the SSS bad AAA stats into the projections. Zips is the only one that projects more than half a season of playing time and they project 1.8 WAR.
For Galvis the 3 projections are: 665, 662, and 669 with the Zips WAR at 1.0. There is no guarantee that this will happen, but the main point is that 3 different projections for JP all show him equal to or better than Galvis today and he has much more improvement in front of him. Which reinforces the point that if the Phillies were contending today, they would want Crawford at SS. Ready today does not necessarily mean 100% developed. It could easily mean 80% to 90% as long as he is at least as good as Galvis and is the type of player (polished) that can develop at the major league level almost as easily in the minors.
http://www.fangraphs.com/statss.aspx?playerid=6609&position=SS
http://www.fangraphs.com/statss.aspx?playerid=sa737507&position=SS