I've played some pretty good Peaches. When I say that, I mean to say that I've played pretty extensively with DoH, and we have had some incredibly good matches. In all the times I've played him, I've found that catching turnips and using them has had little help in the matches. In fact, when I've caught them, I realize that I then have to get rid of them before using my C-Stick for aerials, which hurts me far more than the benefit of catching the turnip. I find that using Ganon's large hit boxes on his aerials(fair, uair) when a turnip was predicted worked better because it often times killed the turnip and in turn hit the approaching peach that was predicting the turnip to stun. However, when not done properly, hitting the turnip merely to deflect the turnip itself can leave Ganon in a compromised circumstance.
tldr: I had more success from hitting the turnip with an aerial when properly spaced, and perhaps even hitting the peach as well as they would try to follow up behind the turnip with an attack. But be careful about doing so.