It's important to have the right cards in your deck, but it won't help you at all if you never draw those cards. But the first time you fight someone with multiple draw supporters, like Miriam or Professor's Research, you'll lose. Provided your opponent makes the same mistakes, you'll end up having a fairly equal match. The latter is also an easy trap to fall into, as it's a reasonable reaction to see your Pokemon's energy costs and fear the worst.
The former mistake is understandable after all, it's the iconic nature of these critters that has printed billions of dollars for decades. When players first start building decks, they often put too much emphasis on Pokemon and Energy cards.
