Kanna Skill Build

Personally, I found Shugyoku no Juin (Soul Shear) extremely useful and maxed it 3rd (after the 10/5 point skills.)

Maybe it's because I love Meso Explosion so much.
The skill is just like ME, but it ATTACKS ONLY WHERE MONSTERS ARE! That was the only bad thing about ME, no seeking.
So it's a high damage mobbing skill that has crazy vertical range and allows you to stay on your current platform. Crazy good. I used it constantly at Jesters.
The only bad part about this skill imo is the huge MP consumption especially for a class like Kanna.

The issue here is how you guys train in GMS.

In JMS, there's no areas to go to that the monsters are so much stronger than you that Shugyoku no Juin is actually even usable. The first situation I made use of it was at Zakum when I was 110 at the time. In GMS, you guys have Jesters and stuff which you go to long before you're at the point where you would level it in this guide and they are much higher level than you, resulting in it being useful much earlier.

It's certainly an option due to this, but in my opinion having your regular attack skills ready and maxed earlier really does it's thing before Juin. Plus, there's the case where people don't go to Jesters and whatever else crap is in GMS to super train, and therefore is useless to them if they play that way.

In the long run, the speed of training at those areas in GMS makes it really a mute point, because by the time it would really matter, you're already leveled and maxed it. How long are you really at Jesters for, or even in 3rd job? A few hours? It doesn't really matter.