Toxic solo players are not welcome in league.
Premades are just as toxic as solo queue. It only takes one person to get it started, then the rest usually join in. It has little to nothing to do with whether or not you queue with someone. It has everything to do with whether or not that player is an asshole. Solo/premade does not change that.
Those players who want it to be all about them, and their performance.
That's most of League, solo or premade. Getting rid of Solos won't change this.
Those players who want to ignore their team until it's time to blame them for stopping their 'carry'.
Premades tend to ignore/blame solos more than solos ignore other players, since solo players have no safety net to rely on. They have to cooperate with their team more than premades have to cooperate with solos.
That's also not how League has ever worked. It's always been a team game and Riot has always buffed/nerfed to keep it in that direction.
It was a team game before Dynamic Queue, and Dynamic Queue hasn't made it any better or worse in that regard. It just made it worse for solos.
Dynamic Queue punishes TOXIC players that NO ONE aside from other toxic players wants on their team. It rewards the solo players who know how to play with a team.
It doesn't reward solo players. Solo players like that function just as well, if not better, in Solo Queue because there was less organization on the enemy team. It punishes solo players in general. For every good experience a solo has in Dynamic Queue, there are a dozen bad ones. That said, good or bad, its pretty uncommon. Most experiences come out neutral. The bad experiences turn out REALLY bad though.