Fifty percent of Yaz was better than 100% of his bench replacement. Also, the opposition never knew how badly he was hurting, so Yaz in the lineup made the pitchers pitch differently to those around him. I believe that 50% of Carl Crawford or Ellsbury is better than DMac hands down. There's no question about it. Plus, Ellsbury and Crawford would bring the speed factor that DMac doesn't have. No, the sitting out when your injured crap is all about preserving stats for the next contract. Better to not play than play below optimum level for the next contract.
Roger Maris played with a broken wrist one year, because taking him out of the lineup would have resulted in Mantle being intentionally walked all season long. It worked. Maris was still considered a threat, and the opposition just thought he was slumping.
As for carping if the injured guy does poorly, you are addressing that to the wrong guy. If a star plays injured, I applaud him no matter what he does. I realize that big stars play better banged up than the average bench player. What would you rather see a banged up Pedroia or a healthy Punto. Star players get paid mega bucks to play, and IMO, if they are physically able to play, they should play. They owe it to the team. I don't care what JD Drew's OPS was in the 110 games that he played each season if my team didn't win and we had to play bums like DMac et al causing us to lose games. That's just an example-- and not a factual one, but it is meant to illustrate a point. If I spend hundreds of dollars taking my kids to see their hero Pedroia, I don't want to see Punto playing because Pedroia has a tooth ache. Again, this is hypothetical. Players have a responsibility to perform for the fans. Some fans say screw that. The players don't have to play for the fans. The fans that say that never buy tickets and never take their kids to the games. Players used to have that mentality that they played for the team and the fans. Today, they almost exclusively play for themselves and they pamper themselves. It's just my opinion.
When I was a little kid, I wanted to see Mantle and Mays. They were both at the end of their careers, but when you went to the ballpark, they were almost assuredly in the lineup. Mantle was severely injured almost all of his career, but he put on the uniform and played if he could walk. I remember seeing him play. It was a thrill. He was a shell of himself, but still better than anyone on the Yankee bench, and benches were much deeper in those days. I remember Mantle, but I couldn't tell you the name of his backup.