When I was playing ranked earlier this season with my friends (once I got into Gold 5 I stopped playing Ranked, mainly because I prefer casual Normals with my friends, but also because season rewards have historically stopped at Gold and above), we played in 4-man pre-mades. As something of a "team leader", I made it a point to remind them that we would need to work around the random 5th player. If the random didn't like their role and wanted another one, we'd let them have it. If they played AD, we made sure to compensate with AP, and vice-versa. If they picked a strong teamfight champion like Malphite or Wukong, we picked champions that could supplement that.
If the random didn't group for team fights even after it was obvious that we needed to (and made it known to them), we worked with that instead of flaming them. There were a few games where the random realized we were pre-made and started flaming us (because I understand the stereotype around the toxic 4-man) but we never let that bother us and continued to work with them as much as we could. Instead of making the plays centered around our group and using our ability to speak and coordinate to each other to allow US to win, we used our communication to facilitate the RANDOM to win, and therefore ourselves in the process. We won most of the games we played this way, and I actually kind of started liking Ranked again.
I don't mean to speak for all 4-man pre-mades, as I know there are bad ones out there, or else the stereotype wouldn't exist, but I do wish more of them operated how my friends and I did. It kept the game fun and not frustrating and toxic, choosing to focus on the variable instead of the constants in our equation.