Valor would be the stat to use, it's the only thing players can't abuse. Gear can be manipulated easily. Match making should be based on Valor, but not by some minimum hard cap. Say 70+'s are prioritized together, but not completely locked out of lower Valor games.. Wouldn't want queues to take forever either!
People need to be paired based on gear level and skill, Valour doesn't prove either of those. The well geared players need an incentive to play together, if people actually started playing Ranked Warzones competitively, then they would start to get paired with other teams with similar ratings. Problem solved.
However that will never happen unless Bioware makes WH gear easier to obtain. People aren't going to put up with the grind, not that they face in Normal Warzones currently. Hell people have not put up with the grind and left already.