I really don't think that /Rad would be OP on a MM, unless /Dark is OP now. Rad and Dark are pretty comparable in output, and in fact, I think that /Rad loses a bit for MMs since the +Recharge bonus from Accelerate Metabolism is not as useful to them as for other ATs, since the henchmen cannot benefit from it.
Kinetics should also be fine. While it's strong offensively, it has little to offer on defense other than a good heal, and that causes a couple of problems:
1: Henchmen need to stay grouped up and near the enemy in order to benefit from that, which is sometimes difficult
2: MMs using reactive healing as their main defense for their henchmen are going to have an issue when the Tier 1s get 1-shotted, or if the heal misses.
The only issue would be /Cold. Cold is a bit strong overall in its stats, but it's balanced by being so weak soloing at early levels. But for a MM that's not relevant, since the MM gets to use the ally shields from Level 1. I'm not sure that Cold really IS OP, since MMs get Storm and Storm is reasonably comparable... weaker on defense, but stronger on offense. I would rate Cold as stronger because MMs get such a benefit from a fire-and-forget defensive set like /Cold compared to /Storm's use of Hurricane and spamming O2 and Gale for defense, but I don't know if it's all that much above Storm that we can say that /Storm is fine, but /Cold is OP. For a good player, they're about as good, and for a weak-average player, Cold is just easier to use. So in the end, I think that /Cold is not OP as much as easy to use.