Auto-Fill is like putting a Silver up against a Plat.
They're just going to get outclassed. I'm certainly not a Platinum Mid or Top. I got to where I am playing predominately Jungle and the occasional Support. If you auto-fill me mid and I get stuck playing against some Syndra one-trick, there's no chance. Apart from my general macro play, I may as well be Silver or Bronze if you stick me in a non-preferred role. I'd rather wait 10 minutes than waste 20 + the time spent earning the 15 LP you just made me lose because you auto-filled some horrible Annie mid.