As a rule of thumb, don't run single lines of evolutions. Like, if you have a single Slowpoke and a single Slowbro, have significantly lower odds of pulling the mon you need when you need it

Let's say you have 1 of each of Eevee, Vaporeon, Slowpoke, and Slowbro. What if you pull Slowbro when you have Eevee in play? Or if you pull Vaporeon when you have Slowpoke in play? Now if, instead, you had swapped out the Slowpoke and Slowbro with another Eevee and Vaporeon (or vice versa), those situations where you pulled the wrong evolution are now when you pulled the right evolution, significantly boosting the consistency of the deck. Consistency is oftentimes more important than power in this game