You're not alone!
I think having a kind of durable off-healer/support/melee DPS (of course leaning more toward healing than dps) can work and fill a niche not be overshadowed if you take in its full capabilities while also not overshadowing anyone. Taking the concept of that revolver-sheath art, the sam's weapon could actually be a trio of swords that can stand for each stance: a spirit stance, a technique stance and a savage stance (given proper japanese/samurai-esque titles) with a draw-out/blade sealing iaido mechanic meaning, if you seal the weapon before resheathing it (to swap stances), you have the capability of using strong draw-out techniques for a time upon activating/swapping into one of the three stances. The catch is, you can't seal into a draw-out...that is, you can seal the current blade when combat ends or seal the blade by swapping to another sword but doing that means you just swapped without using the iaido draw-out technique. Basically, at any given time during combat, you can only have 2 sealed blades at a time thus 2 sets of draw-out abilities with exception of the start of combat so long as the previous battle ended with 2 sealed blades and you seal your last blade. There could be a high level skill, of course, that can be used out of battle that seals all your blades, useful for boss fights.
As for what each stance could do, that is where I'm too ignorant of the games' mechanics. But the spirit stance could allow for healing, heal over times, status removal and its draw-out abilities could be a powerful rez skill, defensive utilities like block/parry bonuses, recovery of mp/tp, etc. The technique stance would have unique support abilities centered around TP (like a tp shield that converts hp damage to tp damage, tp recovery, etc) as well as personal defense with the draw-out abilities having movement abilities, a block utility. The savage stance would be simply damaging skills with a debuff to increase party dps and the draw-out abilities being a strong single target attack, an AoE attack and perhaps a personal damage buff.