The type is usually a basic land type, like Swampwalk, but can also be a supertype, like legendary landwalk on Livonya Silone
Conqueror will obviously see plenty of Commander play, but its actually quite well-positioned for Standard too
Note that fair decks can have draws where they just need a general non-specific type of card off a cantrip
Its not free, but zero mana is zero mana, and thats worth something I guess
The more important reason Gaddock was contained was that green wasn't a natural fit for the decks that wanted Gaddock, or in some cases green was but white wasn't, and his legendary status made it difficult to go too far out of the way to get him
I only look at the commanders that focus on milling opponents and work off opponents graveyards rather than self-mill