You don't have to win consistently. You have to win more than you lose. Even 51 wins to 49 losses is still advancing. The team you get is RNG, but it's RNG for everyone. Everyone is drawing their teams from the same pool of players, your opponents aren't hooked up to a secret queue that only matches them with gods. The only thing you have control over in each game is yourself, so all you can do is do your best and eventually that will reflect in your win rate as you play with all kinds of teams and matchups. As the variables get averaged out over hundreds of games, your own influence is what remains. No one is unlucky forever. If it was pure luck of the draw and your own actions make no difference then everyone would have perfect 50% win rate regardless of what they did.

The point regarding players not yet knowing what to do is that the seemingly binary steamroll or get steamrolled outcome is something that will improve in time as players improve or drop out of the system. Player skill will gradually even out and matches will become less one-sided. But even right now, it's not so absurd that you can't make a difference, and like I said, those players are getting put on both teams.