The 70-74 bracket is the primary twink bracket (imo) for disabling experience.
There are a massive number of players at this level range.
Queues are relatively fast.

Your level 70 PvP gear, is basically best in slot, with the exception of a bit of Sunwell gear.
A weekend of battlegrounds, gets you gear that will never need to be upgraded ever again.

And there are a lot of compositions that can dominate in that bracket as a boxer.
Far more than at 80-84 or 85.

Plus if you want to arena, so stick at 70th with your team.
An equal number of 74's won't automatically beat you, every time.
Try saying the same, for a boxed group of 80's against an equal number of 84's.