A premade on discord will always have an advantage regardless of elo.
But it is a small one.
I play both, in premades and with randoms.
Communication with randoms is a problem only if they are too low level, otherwise I really had no problem communicating, but then again, I actually put an effort in some basic communication and coordination when I see the random is of right communication capabilities.
I've beat multiple premades of similar elo while playing with randoms, so I'll just say communicate better and observe map better.
Hell, even if your team mate ignores you, you can still be aware of what is going on on the map and assist for push or defence, which I'm also doing when possibility arises.
Just like randoms are random, premades communication and coordination also is on a mixed level, sometimes they do it very well and get you stomped, sometimes they don't and you stomp them.
Just today, I was clapped by shit talking premade, next game got them again, instantly told team mate about it and about their strat, so when they came we were prepared and pushed them back without much of an issue.
ELO difference and willingness to communication defines if you will have easier time or harder, not being premade or random, tho being premade has one advantage of always knowing capabilities of your team mate.