Canni 3 is useless.....why?

[Luthandrias]

I hope this isn't a repost. But here are some numbers regarding Canni

Cannibalize 1 takes 50 health and gives 20-28 mana (depending on lvl). So the ratio is 2.5 hp for 1 mana at lvl 24 and 1.78 hp for 1 mana at lvl 60.

Cannibalize 2 takes 67 health and gives 30-36 mana (depending on lvl). So the ratio is 2.23 hp for 1 mana at lvl 39 and 1.6 hp for 1 mana at lvl 60.

Cannibalize 3 takes 100 health and gives 39-46 mana (depending on lvl). So the ratio is 2.56 hp for 1 mana at lvl 54 and 2.17 hp for 1 mana at lvl 60.

Is it a mistake that canni 3 has a worse ratio than all of them, making it practically useless?

Can it be fixed/changed?

Proposition:
change the ratio on canni 3 to something like 100 health for 48 mana (@ lvl 54) and 100 health for 66 mana (@ lvl 60) for a ratio of 2.1 hp for 1 mana at lvl 54 and 1.5 health for 1 mana at lvl 60.

I don't know any shamans who are so lazy that they would prefer canni 3 over 2 when having mana matters.

Cannibalize 3 (as it stands) is pointless.