The size of a premade team isn't the big factor. It's entirely their coordination and skill.

I tend to be rather up close and personal for a ranged. It's almost a signature technique of mine now to run past a lead attacker from the enemy team, or a healer in range, and Blank them back into my party while marking them, and my team usually follows up well. Much of what I and other premades do has been shared in the guides I posted here, so the information and strategies is entirely available, and possible with randoms besides.

Besides, the answer shouldn't be to limit the ability for skilled players to team up, but to instead strive to improve the abilities of ourselves to be considered one of those skilled players.