3rd Edit: I want to ask something about Youmu regarding the subclasses, since I am currently editing the wiki to give some recommendations on what subclasses would be best for her. I am currently considering the following...
Recommended Build: Tank
Primary Stat focus: HP, DEF, Elemental affinities.
Guardian: Stat boosts and damage reduction, and Efficient Concentration and Shield Defense to synergize with Meikyo Shisui somewhat(provided that Youmu has built up enough of a SPD buff beforehand to be able to cancel out the SPD debuff, and then focus to regain Meikyo Shisui).
Monk: Body Revitalization has synergy with both her Regeneration and Meikyo Shisui skills and Dexterity Training can reduce the time taken by most of her actions(attack command can be used to quickly gain another turn without using MP).
Healer: Heals the entire frontline passively, reduces her FIR weakness to almost neutral, and the healing spell is useful for when her regen isn't enough(The buffs from Meikyo Shisui will strengthen the spell a good bit).
Strategist: Reduces the decay of the frontline's buffs(including Meikyo Shisui), applies other effects, including a damage reduction effect, to the front line without burning any MP.
Transcendant: Boosts her stats(all boosts other than MAG are useful here) and reduces damage taken via Enhanced Combat.
What do you guys think about it?
Think I might have a good enough grasp on how the game works to be able to give input on this kind of thing (though I haven't personally used Youmu so I might be really off the mark, just speaking generally here). More or less, for a tank, the most useful things they can be doing (besides not dying) is switching and supporting, since they need to invest most/all of their stats in HP, DEF, and/or MND so that they can reduce damage as much as possible. With that in mind, I feel that Herbalist and Strategist would be the best subclasses for Youmu (at least in the main game, can't speak for plus disc yet), Strategist moreso since Herbalist requires Youmu to spend MP, which means losing out on Meikyo Shisui. The 10% damage bonus/reduction to the whole party is one of the strongest subclass effects in the game and gives an effective reason for using Youmu as a dedicated tank/switcher. Guardian and Transcendant are actually fairly redundant, as tanks generally have good enough defensive stats to be able to withstand attacks to a reasonable extent (~20-30% from the strongest attacks I'd estimate? might be overestimating), so it's usually better to go for something else unless you really do need the extra DEF/MND to survive. Similarly, the Monk subclass does not really help outside the small 4% HP regen/stat bonus per turn, since tank Youmu would ideally just switch characters (and Dexterity Training generally saves 1-2 ticks on anything that isn't too big a delay to not switch out), and the buff is outweighed by the complete lack of stat bonuses toward HP/DEF/MND. And Healer's healing would be much better done by a party-wide Enhancer or a character that has heavy/max investment in ATK or MAG. The extra resistances certainly are helpful, but equipment generally does that better.
So basically, that leaves just Herbalist and Strategist as having strong reasons and relatively lacking in flaws to pick them for Youmu. Well, mostly Strategist. The basic idea I've found for Strategist selection is to figure out which character is accomplishing the least at any given moment in the frontline, which is normally the tank. Youmu particularly benefits as a tank from being a Strategist compared to other characters because Meikyo Shisui encourages her not to expend any MP. A Strategist is just fine being a dedicated switcher. Though, I'm also working with the assumption of an Instant Attack character being present in the party (and honestly, after playing with one, I just can't imagine not having an Instant Attack character, it's an insanely good skill for decreasing the party's downtime), which greatly increases the value of having a character ready to switch frequently. Youmu seems like a fairly self-sufficient defensive character, with Desperation, Regeneration, and Meikyo Shisui being the key skills (isn't Desperation actually a great skill? seems to go under the radar a bit), plus Those who Live in the Underworld giving an incentive to specifically use her as the tank against Ghost bosses over other characters. Dunno about her MND though...since the characters I've been using as tanks (mainly Tenshi, Iku w/ Hisouten Guard, and Momiji to a lesser extent) have well balanced (and high) defense stats, I don't know how bad it being so low is for her. I could just manually calculate it (I do this for every boss for important/common attacks), but gotta check in-game and stuff for that.
I think Meikyo Shisui shows its value most effectively with Strategist Youmu, since it's the only job that can be done without expending any MP at all. Meikyo Shisui effectively becomes an extra strong Majesty in that context, and being able to buff her DEF/MND and her SPD helps in the switching role. Regeneration and Desperation probably provide enough of a buffer that Youmu can invest in SPD instead of defenses to some extent, depending on how much of an impact Desperation's buff has for reducing damage (useless for defense ignoring attacks, for example), so she can aim to more reliably switch characters after they attack. Meikyo Shisui itself accumulates quite quickly, netting a 45% buff after 5 turns and 66% after 10 turns (assuming Strategist), so it's pretty significant.
But I'm just basing off experience using other characters. Using Tenshi, I just have her use Enduring Celestial + Keystone Formation and never need to buff her defenses in order for her to tank as a Strategist (I've yet to find a practical use for State of Enlightenment tbh). Youmu has less DEF and a lot less MND, but she has Regeneration, Desperation, and a higher buff baseline, so I'm thinking the same principle should apply for her (at least for DEF).
EDIT: Ah yeah, by the way, I don't think it's a good idea to try to mention a bunch of different subclasses. Usually 1-3 are just plain better than anything else you could want, and in this particular context, I'm struggling to see a good reason to use anything other than Strategist if you want to have Youmu be a tank. Like, yeah, you could do something else if you wanted to, but if it's a question of effectiveness, comparatively speaking, I don't think you're really going to do better than Strategist in any context that exists in the game. This is just my opinion, but I think things like guides and recommendations should be narrowed and focused on what works best.
