I think you're selling Cthulhu a bit short there.

Yes, Cthulhu's C frame misses, but with 6% Affliction it's not bad. With 6% Affliction and debuff-, it's reliable, though not 100%.
Orb removal is very powerful, though also very unreliable.
And finally, Cthulhu has Charm. A very potent one at that. Sadly, again, unreliable.

The combination of these three make Cthulhu a very potent package. Sure she might not deliver the best she can every time, but hardly ever will there be a time when all three miss.