The definition says that it is used when we want to emphasize the fact that two things look so much alike that you can't see the difference.
Now I personally like to look at the root of the words when learning them, so I learned to see まるで like something that includes the thing it refers to as a whole because of the meaning of 丸 (round shape, circle). So I'd usually translate it by something like "complete(ly)" (I'm not a translator though) which I think carries more or less the same meaning.
丸で地獄だ : It is complete hell
When added to (か)のように I feel like it adds the same nuance of taking what follows as a whole and although sometimes it sounds more natural not to translate it, I would still see it as "complete(ly)".
I assume you learned this grammar so I am not going to go too much into it, but 様 carries the meanings "way, appearance" so if you want to see it in a literal way you can translate it in your head as "in a way/appearance of..."
か is, to me, a particle that shows uncertainty. In the case of かのように, I feel like the か is what gives the expression this meaning of "as if" (something that is thought to be unreal).
To sum it up, this is how I would translate (literally) the expressions in your sentences:
まるで天才のように : In a way of completely a genius (like he's a complete genius)
天才であるかのように : In a way as if he is a genius (as if he were a genius)
天才のように : In a way of a genius (like he's a genius)
まるで天才であるかのように : In a way as if he is a complete genius (as if he were a complete genius)
This is how I make the distinction.