@ringkichard
I did the math a slightly different way but ended up with the same result as you did.
Also, after playing a match today, my faith in quicksand is restored. I used it on a hydra that was guarding the enemy mage. The hydra escaped on the third roll, but that gave me 2 free attacks on their mage without having to worry about a guard. Not only does quicksand force them to waste actions, but it renders the target immovable and restrained, something I definitely overlooked. As an additional bonus, quicksand is a conjuration, which means there is no real way to prevent it; nullify only works on enchantments or incantations!
Long story short, I run 2 quicksands in my warlord deck from now on.