With Ensnaring Bridge and Moat you could still attack if you had the right type of critters.
No, you don't need Light Quantum for Sundials to be effective.
ex:
-You only have 1 Oty out and need to stall for time to start eating your opponents critters.
-You're missing 1 quantum to cast Rain of Fire, so you stall for a few rounds.
-You're opponent is about to kill you, or deck out. So you stall so your opponent decks out.
And that's just a few cases where I've used without actually activating Sundial...
And if you have enough damage on board to kill your opponent, chances are that Sundial wasn't going to help him anyway...
Speaking of MTG, does anyone remember White's "Circle of Protection"? For the cost of 1 mana you can negate damage from any 1 source of the color named on the card. So even if your opponent had 30 critters on board, for the cost of 30 mana you could negate all damage taken. But, there were three ways around this. 1) Either destroy artifact, or 2) Direct Life Loss, or 3) Play multi color decks/monsters.
Sundials?
Destroy (Grav/earth), Steal (Darkness), Fallen Druid to hopefully get either of those two abilities..., Direct Damage (Fire, Darkness, Death, Water)
Quantum towers?
Destroy, Trident, Steal, Pests
Someone said this earlier, I think, but every card really does have an opposing strategy. The big problem is, are you playing that strategy? Its akin to the people who were saying how hard Scorpio and Morte were, but still refused to put purify in their deck. Or how difficult Seism is, but don't have Protect Artifact. Sometimes you have to lose....