@Laxadarap - I can reserve this question and ask - Why today rainbows must have easy way to PC? Explosion, Steal, SoF and more...
Yes, PC should be difficult to use, especially for rainbows. Rainbow decks has got too much advantages, they didn't need "easy PC". Life, Air, Time hasn't got PC, so technically there is no problem to disable PC for rainbows.
What is more - Steal in mono darkness maybe isn't the biggest problem in game as Steal in rainbow deck. When mono darkness steal Hourglasses or Mindgate then both players can't use it. But when rainbow use Steal...
It is very difficult discussion, but necessary. There are too much destroying cards in game. Few elements has got PC and CC (like Fire), Life has got nothing. And here is a question - add PC/CC for Life or throw out PC/CC from Fire. All Players know that Zanz didn't throw Explosion, so they want to see PC for Life, Water to balance the game. I suggest third way to solve this conflict - making PC and CC harder to use. How? Raise the cost, protect by Marks or other concept.
OldTrees mention about taking risk by Players. OK, I accept this sentence and I give next reason for "buff" marks - Player should choose level of risk when he choose mark. Light, Life, Air should protect me against destroy tactics. Fire, Darkness should promote destroying but gives more risk.
You want to use PC? There is no problem, choose Fire mark, but opponent can also use it.
You didn't want to play against PC? There is no problem - use Life Mark. You can't use PC and opponent also.
You didn't want to play against thousands of BlackHoles, Pests or Quicksands? Choose Light.
You didn't want to see tones of CC? Choose Air
You want to draw cards faster/or see next 5 cards? Choose Time
etc.