Hard disagree. 3 teams is the only guarantee that the winning team doesn't snowball to victory instantly as soon as they've won their first engagement.

If your teams are constantly piling on the 3rd one on NA, I don't know what to tell you, your players are doing it wrong probably. I'm not gonna pretend it never happens on EU - and most of the time it would probably be due to unfortunate node spawns - but in my experience in the vast majority of cases the winning team can expect a visit from both losing teams relatively soon if they're leading comfortably.