If The Pit didn't have a single target DPS check, it wouldn't have an identical "Meta" to The Tower.
EVEN IF the game was better balanced, the META would remain so limited because virtually every mode contains the same formula:
Clear speed/Trash Mob check > Followed by a single target DPS check.
I'd suggest the following to actually expand build variety.
The Tower - Remains as it is, requires a balance between clear/single target with a 10 minute time limit.
The Pit - Remove the single target dps check, make it a full clear speed test, once you fill the bar you've completed that tier, with a 10 minute time limit.
The Arena - Fight 3 random lair bosses back to back, with a 10 minute limit.
All 3 modes would scale post Torment 12, like the Tower/Pit does now.
Meaning you have three different METAs to push at Endgame and you would significantly increase build variety.