This is highly unlikely scenario. There will always be new tiers of gear and people will always want them. The idea that people would use a buff to get their WH gear set in 15 matches instead of 20 and then for some reason quit the game is not very well thought out. Someone who wants to gear up and unsub is going to do it regardless of whether there is a comm bonus or not. In fact those players as significantly less likely to purchase the buff since they have already decided they are canceling their accounts.
Did you forget that your suggestion was F2P = unlimited warzones? If not, why are you equating unsubbing with quitting the game?
The scenario is 1) get full WH as F2P with comm boosts, or subscription till full WH 2) stop paying but continue playing unlimited warzones for free.
Your whole argument is based on gear as an incentive to pay/sub, but the incentive is simply not strong with how minimal the difference is between WH and EWH.