Yes, I don't disagree with either of you on any particular point. Obviously most of what I am saying is going to be colored by my experiences with my cube and my playgroup. I have never seen a mono-color deck played from my cube. Never. I would say the most common is a 2 color deck with a splash of a 3rd.
Bottom line, if you have a CC card and a CD card, the CD card will only be easier to cast if you have exactly equivalent amounts of land. How often does that happen?
@Dom I guess you would have to use numbers to say what you mean. But if you are playing a CD deck with 10 C lands and 7 D lands a CC card will always be more castable than a CD card, right?
What Dom is saying is that the DD card will be less castable than CD. In your 12/5 example, MUCH less castable. It's always easier to splash CD than DD.
A two mana card example. Results are probability of casting on curve. Assuming we are on the draw, so 9 cards seen.:
CC at 10/7 = .73 on curve
CD at 10/7 = .86 on curve
DD at 10/7 = .50 on curve
Also, CC cards only get significantly easier to cast at 12/5, if we keep our basics-only assumption. You'll see the CD is the easiest to cast here.
