The reason Shoha is level 80 is because you're -very- likely to be able to use a double-iajutsu in the level 77 and 79 dungeons, but it's highly unlikely you'll use meditate in the level 77 or 79 dungeons.

You're -very- likely to use meditate in Primals or Raids, where such downtimes commonly occur. Would you give up the ability to double iaijutsu for shoha in levelling?

Didn't think so.

But Shoha is really good. If I told you 'Do 815 potency in your first gcd after downtime ends on a boss fight' any samurai worth their salt would appreciate that.

Well, that's what Shoha does.