I think the problem is that new cards make mill very easy. Mill half of your library with a single card, sure. If you are playing blue it's easy to counter, but what about other colors? And the worst thing is that very often, when you playing against a mill deck the ruin crab is in the opening hand of your opponent, causality? At least should be more options to balance this problem, e.g. cards that allow to bring 50% or more cards from the graveyard to the library. This could be an artefact that can be use by all colors.
I think the problem is that new cards make mill very easy. Mill half of your library with a single card, sure. If you are playing blue it's easy to counter, but what about other colors? And the worst thing is that very often, when you playing against a mill deck the ruin crab is in the opening hand of your opponent, causality? At least should be more options to balance this problem, e.g. cards that allow to bring 50% or more cards from the graveyard to the library. This could be an artefact that can be use by all colors.