About the MK only being able to heal itself if it isn't killed in one turn:
The colosals cannot auto-heal themselves at all to the best of my knowledge, whether they are killed in one round or not. Saying it's no good because if you one-round it it can't heal seems a bit off, considering no one else can do that anyway. Eg: the conquest requires a unit to repair at all, which puts the conquest at 21pts minimum if it wants any sort of repair ability. The fact that the MK has built in auto-heal, combined with the fact that it's easier to heal a beast anyway, balances out the lower amount of boxes.
My thoughts anyway!