Physically defensive Gastrodon is another great counter. It plain walls Rotom-W and Genesect, to of the most common Volt-Turners, and resists Scizor's STAB. It can also burn Scizor, erasing it as a threat. Toxic can be used to deal with Rotom-W. Although, it is a bit defensive.
Unfortunately even the physical Gastrodon set is murdered by Scizor's CB u-turns, that do around 45% and if you don't run SpD evs then scarf Genesect's bug buzz will always 2hko.