Sorry to interrupt but:
I can overproduce quantum and save it for later, however with Void I can only drain an opponent's quantum to 0. If you spam something like Void Dragons and Nymphs you can't get pillars out quickly enough to compensate for the gain until several turns later. Also, if you just change your mark all the Void Pillars in a deck become near-useless unless you run pendula.
What Oldtrees is saying is that Void creatures give the opponent mark quantum, so that Void pillars can destroy it. A well-balanced Void deck does not "overproduce" with it's pillars, but does not give the opponent too much quantum either. (Compare this to starting with a hand full of normal pillars and a hand with just 1 pillar). If you want to run Void Pillars in a denial deck you have to sacrifice card slots, and normal cards also cost quantum instead. How many pillars do you plan to get rid off to fit the Void Denial part in? You can't just fill a deck with Void Pillars and expect it win, simply because nobody only runs monos.