Duo's aren't an issue so much as 4/5 man premades, particularly premades that are very much gaming the system. (E.g. 3/4 mains and a smurf that is ~1 tier below the mains, so they get matched against a premade somewhere in the middle of the mains and the smurf, who are in theory all worse skillwise).
I mostly play support as a solo player, and usually not an initiating support (that is to say, I play Janna), so I haven't had any issues with premades* since I can basically follow their lead and it's fine without any need for direct communication. I can see how it'd be somewhat more frustrating for other roles though who really need to coordinate their engages/dives/etc.
*= I (and my team) did get completely wrecked by a panth/noct/tf/vayne/raka comp that was absolutely a premade. Tf would ult (providing vision for everyone) leading to noct ult followed closely by panth ult, with raka ult on standby as insurance. We were essentially getting 4 manned under our inner turret while our outter turret was still standing and it was rough beats. That was 1 in ~100 games though.