#3 - April 19, 2016, 10:32 p.m.
You will not be buying PvP gear from a vendor in Legion. Instead, all gear will be acquired through the strongbox system.
Battlegrounds and Skirmishes victories have a chance to reward you with gear on par with heroic level Dungeons.
Arenas and Rated Battleground victories have a chance to reward you with gear on par with Raids. As your rating increases, the ilevel of the gear increases. So a player in the 1700 range may be getting Normal Raid level gear while a Gladiator caliber player will be getting Mythic Raid level gear from Arenas. Each bracket rewards gear based on your rating in that particular bracket.
Each week, the first few victories in each rated bracket will be a guaranteed piece of gear. Currently, we're thinking the first two victories but it may increase to three. This is not enabled on Alpha due to a bug. It's been prioritized to be fixed soon.
Also, keep in mind that in Legion, your stats are predetermined in PvP instances. But your overall ilevel will increase those stats. The base item level at 110 is currently set to 800. If your gear level is 810, your stats will be increased by 1%. So while better gear does offer an advantage, it can be more easily overcome than in the past.