Look, this happens in about EVERY SINGLE GAME EVER. Even if it is a new game mode, things change and players feel new to this kind of fast paced games. It will take time, not even hotshotGG or bigfatlp know how to play dominion perfectly. Everyone, are testing champions, knowing the game mode, what you can do, and what you cant, developing strategy and independance for small fights of 2 - 3 people per team. You have to be patient.
BTW Riot DID inform in every way posible to all the players about how to play dominion. They've created a whole new website explaining every aspect of the game and how the mechanics work. There have been live streams during the intel masters championship showing how the gameplay was. Showing us entire games of dominion. And there were lots of games streamed. And now we are able to play a BETA version of it before going on to the real thing. Riot published everything in every way possible, throgh the launcher, the website, the home page of the game. EVERYTHING. Dont complain, just be patient and enjoy the game.