I haven't really had a problem with premades lately. I don't know if it is because I play on aether or what, but it's very rare that I witness a steamroll anymore.
The real trouble is lack of awareness imo. Being aware of things is a major problem in NA.
For example, in one match of seal rock, my team was blue and in south. Red team had tons of bh5 and was killing it in combat, yet they got tunnel visioned on fighting yellow. Node rng was good to us, and even when we had 2 nodes and over 600 points, the other two teams just kept fighting up north while we sat on our nodes to win.
Imagine if just one person on red had said "kill blue". With just one line in alliance chat, they could have made a bigger difference than anyone could have hoped to achieve with kills and damage numbers alone. They might have made a win lose difference.
In another match, this time Shatter, we had a similar situation. My team (blue) had 1432 points and our big was up. Red had all the bh5 and 1575 points. Yellow was all in on red.
Our commander took half the team to go pinch yellow! SERIOUSLY!?! Thankfully, the rest of us were able to burn down the ice and win before they could blow it but still...
I kinda feel like I should start taking screenshots of game states so people can see what I am talking about, but for me the general awareness seems a much bigger issue than premades. You can be an absolute gigachad in combat but if you're ignoring callouts and totally unaware of incoming pinches or which team is in the lead, you a liability.