From my personal experience, what really separates 1300 and 1400 player is more skill than deck composition.
With a solid deck you can easily reach 1300 even playing for shit. Above that, you will need the skills to win.
I feel i could reach a top 100 spot if i were more dedicated to this game. Like past week i reached 1300 around Wednesday, which is pretty good (i was top 50 i guess, dont remember), but than, i couldn't play anymore for the week.
Thing is, you need a solid deck and be a good player to reach that 1400 elo
. It takes just a win strike to make it from 1300 to 1400, i dont think it is that hard with a good deck, a good player and a little bit of luck.