Just how much does preseason count?

I would like to know to what extend does playing in the preseason have on your rank in the 2017 season? Say for example you get gold 5 in season 6 and then you play preseason and get plat 5; would you be more inclined to get a higher ranking compared to a person who got plat 5 in 2016 and had the same win loss in placements?