It didn't matter how much crit or haste your gear had, or what trinkets you had equipped, you couldn't use it. To briefly explain how Legion's PvP stat template worked, the only thing that mattered about your gear was its item level. However, we previously datamined the new spell PvP Stats - Spec Stat Template - All Specs (Mage Tower Edition) which is basically identical to the Legion PvP stat template spell PvP Stats - Spec Stat Template - All Specs.
We weren't exactly sure what kind of normalization Blizzard would choose as the Mage Tower has not been publicly tested. BlizzardWhile the Challenges were considered quite difficult for most of Legion, we’re tuning the encounters in Timewalking to normalize player power, with the intention of providing a meaningful level of difficulty to current players.