Basically you can math it out where Canas literally can't die in a lot of situations, and against multiple types of units, if he's using Nosferatu. His only real risk is against very speedy units or light magic users-- either cause they can double him or because Nosferatu can possibly miss.
It's tough to do that with other units without the help of terrain and even then they won't likely be holding their ground against physical, magical, and (reasonably) speedy/accurate enemies all at once. And they won't be attacking all the enemies back they survive against unless it's a speedy (good luck getting a tanky one) magic user (which is why Serra is the strongest and mightiest unit of all the times). That's what I mean by versatility.
I mean I still don't think it's that necessary I'm just saying why I find it more useful than Luna when I actually use him.
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I tried to have a fierce rivalry with SuperNiceDog, but he made me look worse than a GameFAQs Contest!