There is no reason why that sort of deck shouldn't be at Rank 10 Legend. If you face enough slow decks, it's extremely effective to use it.
Also, the likelihood of your opponent drawing the exact combinations of cards that allow them to do that by turn 4 is so absurdly low, that trying to make that a point ruins it. You haven't faced something like that more than once or twice, if ever.
Either way, you already gave away the solution to your problem when you said they spend the first 4 or more turns ramping up mana. That is exactly what they need, turns where you don't do anything. Solution is to not give them the turns.