your right there is a waste factor, but size is important too.

imagine you have a fish the size of a soccer ball, or basketball, w/ poisonous spines, and the tank is not much bigger... now... all other things aside (like the moral aspect of keeping a fish in the equivalent of a thimbul) do you wanna stick your hand in there? I sure as heck wouldn't!!!!

Lion Fish grow fast. all of them.