Luck of the draw can definitely not be underestimated.. I think that's honestly the main difference between budget decks in mythic and more expensive ones: consistency. Very possible to get a good WR with a budget deck, but keeping that up consistently is harder than if you had a more solid deck. New system does make it more welcoming for cheaper decks though: plenty of packs to be earned and legendaries from 15 wins, as opposed to 17 (if I remember..).