This is a good time to explain the difference.
From my understanding, Accuracy is multiplicative whereas To-Hit is additive. So if an attack has a 75% Accuracy, then a 20% Accuracy boost will raise it to (75x1.20) 90% and a 20% To-Hit boost will raise it to (75+20) 95%.
Protector Bots will cast Force Field shields on the other robots and MM. (And possibly other players but I'm not sure, it's been a while.) The Def IO enhances that. Endurance reduction is also good for them since it affects the Henchman casts and they spend a lot of time buffing and healing, which suck up end. All this means that Protector Bots spend very little time doing damage and when they do, they don't do that much anyways, so Def/End (and maybe heal depending on how you feel about it) are typically better on them than Acc or Dam.
While a lot of people are reinforcing the idea that you should just use Pines, Pine's isn't all that great for a few things, especially MM pets and explaining unique IO enhancements. MM pet powers literally just say "summon pet" and don't tell you anything about what that pet does or it's damage or hp. For that, I like to check in game. If you look at the info for any pet power or upgrade power then it will tell you what abilities that pet has/upgrade grants and even let you examine the abilities to see damage, accuracy, end cost, recharge and other values.