Uhh, I didn't JUST point out the advantage, I pointed out that it's a silver lining, and certain champions would become completely nonviable solely because they cannot duo.
Duo jungle is NOT a superior strategy to having an ADC/Support but you're kidding yourself if you think it wouldn't come to that point eventually when people aren't even allowed to have experience working together.
It literally has nothing to do with one player being better than the other, it's that two players must play specifically with each other to gain what's known as 'synergy'.
Kalista is already garbage tier, you seriously think having no possible option to duo would benefit her? Or should we buff her so she can soloq, but then becomes an unstoppable monster in pro-team play? The game is 100% a team game, and duo que allows more viable champions. If no one is going to work together, we already know Master Yi is the best choice.