That's not offtopic at all! XD Anyway, I'd compare Miko more to Nitori. Miko has the slowest leveling rate in the game, and her library isn't cheap either, so whilst she can get tanky, I'm a little dubious- especially considering how potent the other tank options already are. More importantly, she doesn't really have any particular talent in supporting, so even if she can match or somewhat surpass other tanks defensively, I'm not sure what the benefit would be... her heal is strange and has a rather steep mp cost, and whilst she boosts the party's buffs after awakening, it works at 50% in the back too (along with being a good bulky attacker who could stay out plenty, far as I can tell) so, why go for a tank?
Nah, she's moreso for bulky offense. Her set of attacks is a little small (at least before awakening boosts one of them into silliness), but that's what subclassing is for, and her awakening makes her REALLY nice looking for the role.
As for the one asking about Orin, she looks like she's got good potential after awakening, and Koishi looks pretty neat as well; if you're using both you might want to bring Utsuho in too eventually, once you can afford to awaken her. Assuming you don't change your mind about Orin, at least. Satori is... I'm not sure. I'm still wondering if using her in an HP build works or not? With the rest of the Earth Spirits team her stats are brought up enough to be good to keep just attacking as normal, I suppose. She's got high natural HP so maybe with a quartz charm and affinity gear she could be a somewhat bulk-ish attacker, and she can subclass for about any element attack for her awakening that heavily boosts weakness damage. Mmn, she just seems like a character you're mostly using because of earth spirits >.> She does do heavy damage with copying certain attack skills, but it's party dependant.
Just having 3 out of 4 earth spirits members is probably fine, though. >_>