T5 could be the overworld equivalent of a Tier 150 pit. HP of mobs wise.
The new slogan could be: “Unite and gather your strength to defeat the vicious hordes of the T5 world”.
Player 1: Look. Its a small vile one. Oh… Suppressor/Waller/Minion…
Player 2: Oh noes. That will take us 20 mins. 
Player 3: But think of the rewards!!!
Player 4: For the legendaries!!!