Ensnaring bridge had very little limitation around it. If you put ensnaring bridge in a deck that was meant to use ensnaring bridge (burning bridge for instance aka ensnaring bridge, 20 mountains, and 36 spells to shoot at your face), it effectively read: "While this is in play, your opponent's creatures cannot attack.", all the while just throwing anything that was drawn at your head.
Sundial is more or less the same way. In a deck designed to abuse it, it becomes very abusive not because it's a one-way street, but because one deck is designed to abuse it by building up something really damn scary behind it (EG slowly building up Otyughs, fireflies, mutants, etc... the way rainbow does, speed poisoning you, or building up a huge amount of fire quanta to burn you to death in one turn).
However, that doesn't mean sundial is broken. If a card needs a special strategy to "abuse" it, then it's a good card!
In fact, what would happen if we nerfed sundial? It'd more or less always be a race as to who can drop the biggest scariest critters first and outrace their opponents.
Heck, you can make the same whines about aether/time combos. Mono aether time splash for hourglasses and anubis, anybody?