I kept on saying, 'this does deal damage'.
When pairing muramana with presence of mind (and in my case, also manaflow band), mana = damage.
Turns out that I was right.
It was brought up in the LEC broadcast what the stats for it are--a completed muramana could deal 90 damage...compared to the 80 damage of an infinity edge, as the broadcasters said. (As in, did do damage--as in, the person using the muramana was dealing the most damage in the game at that time.)
So I was right.
I am right.
I knew I was right.
Muramana is viable.
So I'll be continuing to make use of it.