Iggy has improved as a hitter but expecting a continual improvement in baseball is simply unrealistic. Hitters improve. Pitchers probe for the hitters weaknesses. They are exposed and they are either overcome or not. If they are overcome they are not even overcome the same way by every hitter though they might seem to have similar if not the same weaknesses.
Pitchers have found the biggest hole in Iggy's current hitting capabilities and they are exploiting it. He will either overcome it or he won't.
WMB will overcome his current biggest hitting weaknesses or he won't. Even if they both overcome them, in both cases, pitchers will continue to probe and exploit whatever remaining weaknesses they find.
This is why some refer to hitting ML pitching as the hardest thing to do in any team sporting activity. If you look at the number of athletes in this world trying to hit thrown baseballs and the pitiful few by percentages that actually reach the pinnacle of the game it is hard to argue the point. There are stronger athletes, faster athletes, more durable athletes but no athletes that have the hand/eye coordination and reflexes of the ML hitter.
Those that do make it and stay in the ML's as hitters are so good, that all it takes is the most meager of decline in the pitcher's capabilities in order for those hitters to succeed. The ninth guy in a ML lineup (if he is not a pitcher) creams crummy pitching...destroys crummy pitching. At any one time, there might be two or three hitters in the entire world that are functioning at the peak of the sport as hitters. How many guys are at Cabrera's level? Are there one, maybe two others in the entire world??? In fact, you have to layer on a willingness to study pitcher's tendencies and understand what he is likely to throw in a given situation on top of tremendous hand/eye coordination and reflexes to be a Cabrera.
I still think the Sox have enough hitting to succeed as a team, as long as Ortiz stays upright. They don't have enough pitching and their defense has holes. Now that Drew has had his three AB's for the month, we could likely sit him and avoid the next 30 AB's. Maybe keep Drew in for the last game in Camden Yards which has even more laughable RF dimensions that new Yankee Stadium. So if they want to try WMB back at 3rd and Iggy at SS I guess I would be OK with it if WMB has actually improved. I am not even opposed to XB at 3rd and Iggy at SS if they have been working XB at 3rd.
Neither WMB or XB is going to light it up in my opinion because past the weak part of the schedule coming up after Monday they will be facing pretty good pitching the rest of the way. Expecting one guy with problems and another guy with no ML experience to come up in that environment with pennant races on and light it up is unrealistic. Maybe it will take some time for pitchers to get a book on XB. So, he might enjoy some limited success.
Sox should get a couple relievers, see if Lee actually comes available from the Phillies and make their run.