I firmly believe the primary reward for playing the game should be the experience itself, but looking fly and having a sweet mount are pretty cool too.
I have no issue with rating-gated rewards, but this being the primary cosmetic reward system is detrimental to gameplay. Anyone who thinks they cannot hit X rating will not bother to achieve X rating. This leads to a lot of players not queuing until late in the season, after inflation has ramped up, creating a subpar early season experience.
Imagine an alternative: You can get a sweet mount for hitting 2300, or winning 50 games above 2200, or 100 games above 2100, etc. This encourages people to just play the game. If you hit X rating - congrats, you get your reward immediately, but if you can’t, just play the game at your own level and you’ll get it eventually. People who play early season get their rewards before people who play late season.
I think the less convoluted way to implement this system is to have a PvP currency used to purchase cosmetic rewards (mogs, mounts, toys, etc.) Where games won at higher ratings earn more of the currency. Every season new rewards are added to the vendor, and some rewards are time exclusive to encourage monthly/seasonal participation. The rewards earned could simply be recolors of old and existing PvP mounts and armor. Even unused appearances like a somewhat notorious Blue Sword 
Additionally, sometimes you want to play with a group friends with various skills levels, and rated PvP isn’t the place to do that. No one should forego social interactions because they’re grinding a cosmetic reward. I think making a trivial amount of currency earnable through unrated PvP wins would be acceptable, even if there’s a weekly cap for it.