Are you serious? I'm not sure if anyone told you, but Grant Hill had knee surgery 2 weeks ago. The fact that he's able to play at all is a testament to his desire to be on the court, and the fact that he's not playing great is perhaps the single largest reason he NEEDS to be in the game as much as possible from here on out. Grant Hill isn't some young player who needs to improve his skills before earning minutes (i.e. Markeif Morris). He's a player who needs to get his rhythm back so that he can re-establish the command over his body and use the skills he has in a playoff-intensity scenario.
Unless, of course, you don't think a healthy Grant Hill is an asset this team needs. If that's the case, then you're probably right: there's no reason to have a player play through the rust and timing issues that accompany mid-season injuries if that player can't be a significant contributor after he works through the rehab kinks. If that's your stance, then I disagree with you, but it would make your conclusion more logical.
I dunno, I just love Grant Hill and what he brings to this team. And I really don't like it when guys like Rudy Gay score in the mid-30's in must-win scenarios.