My favorite Filia variant! This Filia I feel like is a gateway for fighters (especially those using lower level teams) to determine whether or not you are strong and know how to use all modifiers and Signature abilities to your advantage! You either are high enough level to power through her HP and bleed, or use other modifiers (Immunity, bleed, hex, etc) to circumvent her ability to win. Fighter's without those modifiers are in for a very tough fight! ( i.e No Egrets Parasoul who depends on crit values to stop BBs but will probably bleed out) I guess the only problem is that she only applies heavy bleed to critical hits and it can't stack. If I were to change it, I would apply heavy bleed+ (1) stack of bleed per critical hit. That way if you try to power through with critical hits then you would bleed to death quicker! Maybe that's a bit too much though.
I'm having trouble choosing which MA I want to eventually apply to this fighter. Bloodletting may seem obvious since it's possible for this fighter to regularly apply bleed to enemies, but at the same time, since it's a defensive fighter, I'm not sure how effective the AI would be at inflicting a permanent Bleed. Leech, on the other hand, seems like overall a less useful MA, but gives Dread Locks more potential to reflect damage back on opponents by stealing life whenever it manages to pop off a combo. But I don't think I've ever seen a Filia with Leech on. It's Leech truly not at all worth it?
Leech is generally not worth because it recovers (at max level) 15% of damage filia does and most filia variants in general do little damage. Most usually do Bloodletting since french twist can be comboed into blockbusters with a high right of inflicting bleed and converting it to permanent bleed which can be used to carry high streaks for a lot of people. If anything leech maybe is used on defensive Filia but I haven't really seen other Dreadlock filias. Mine has leech on because I like the synergy of it. Maybe if it was similar to Assassin's Greed's 2nd SA or if the amount regained was increased it'd probably be worth it.
If you're gonna use this variant to try to carry you to streaks then Blood letting. And as you said the AI are sort of not efficient at dealing permanent bleed so, in my own opinion, if you're gonna make her super defensive then I suggest use leech. But like I said, it's how you wanna view her.
Things that you might wants to build:
HP, Block Proficiency, Meter Gain, since this enhances her ability to survive and deal a lot of damage.
Recommended PFs: Valentine, Eliza, Miss Fortune.
Recommended Rift Battle positions: Immunity, Regen, Armor and Biofeedback.
In general, you will want her as the first fighter of a team with someone who can respawn her if she gets KO'ed. A nice team for her is GI Jazz and General Surgeon, and she will do incredibly well with maxed meter gain, since her BBs will charge with the hits her teammates receive. And Big Band can take a lot of them.
I've always liked the idea of Leech on a defensive Dreadlocks. She doesn't deal a ton of damage, but healing is still healing. Without meter control and careful playing, a defender with a BB3 will hit you with a BB3. Lucky for Filia, she has two. And, once you get up to higher streaks, that damage is boosted a lot. It makes more sense to use Leech on her imo but The First Cut wouldn't necessarily be bad either.