Anecdotal evidence that the melee-only mission is retarded
First off, let me say it's absolutely ridiculous that you only get 5 tokens for finding a whole premade who will agree to play, at best, 5 games without a ranged champion before matching puts them against either another team trying to do the mission or a group of glue eaters for a chance to win.
But I just had a game where the enemy was clearly trying to do the mission (same clan, no ranged), and I lost connection early on.
I came back, my one friend who was premade with me has died 10 times, and my team was only behind one kill and winning in towers. We went on to win the game.
Melee only is such a stupid mission that it loses a 5v4, even with the assumed-but-untested advantages of having a 5 man premade group, AND both Yi and Nasus for the late game strength.