Those reports are handled the same way regardless of if a 5 man or 5 solos are reporting the person and you know it. Do we need to remind you that you asked for sensible comments?
Dynamic queue premades are 3+. Possibly 3 friends who enjoy the concept of free elo or want to play ranked for fun (to the detriment of solo players). So yes, making their votes count as one is the best way to go about it. It even makes the results more statistically correct.
You're so clueless it hurts. It literally hurts.
What's the problem with premade groups in Normals? You can't be competitive in Normals. You're with and against players that are trying new champions, builds, and roles, and matchmaking spans across every rank.
If you like playing with your friends and you want to be competitive, playing the best games you can, then you'd take your premade to rank. It has nothing to do with trolling others or free elo, it has everything to do with wanting to play a better game.
It's also not "statistically correct" to clump people together based on if they play in a premade or not, it's a statistical nightmare!
Player X only plays Ranked with his friend, Player Y. Player Y plays 90% of his games solo, without Player X. According to you, Player X shares Player Y's vote, but Player Y doesn't share Player X's vote.
Now imagine that same complexity across multiple groups of players. You've got a giant mess of data that, at the end, tells you absolutely nothing other than "there were people, and they voted."