If you compare magneton to trio, it's not bad. Trio traps everything. EVERYTHING. Magneton doesn't, so you can't ban it on that reason.
I don't see much different combos unless it's vap. I could be wrong, but usually that's the one of the very few people use to counter it. In the split, most of the ou walls in gen3 wont be able to take much from it. Not everyone builds their team for one poke, and if you plan on using 2 or 3 pokes for a counter of one, wouldn't that mean that the poke you're trying to counter is op? I think i stole this from someone.