Working on a new post for the blog. I was supposed to have Morrigan/Vergil/Doom up 2 or 3 weeks ago but I've been half sick, half lazy. Probably going up this Tuesday. Overall balancing the game is an exercise in opinion more than anything.
Nerfing characters like Zero and Morrigan would be really tricky. I think Zero needs a nerf but completely taking LL away from him isn't the answer. Zero/Doom can easily break 1M off a pizza cutter or assist without LL; the basic BnB I do on the Zero/Doom/Phoenix team does 650k+ without a super. That's the problem right there. Zero is supposed to be a low damage character but even if you took LL away from him he could still easily ToD relevant characters off common openings (stray buster, low B, pizza cutter, etc). Probably the best way to balance Zero would be to change his damage scaling. IIRC his minimum scaling on specials is 30% and normals is 20%. If you cut that in half (for example Wesker's minimum is 10% on specials and has no minimum on normals) his damage becomes more reasonable and he doesn't ToD everyone in a meter positive way.
Nerfing Morrigan seems easier. Her fireballs have 5 durability, each one does 25,500 on chip, astral vision is 590 frames, she builds meter during astral and shell kick is Haggar pipe that's harder to air throw with a 5f startup. If you take 2 of those away (any 2) she becomes more reasonable. Personally I'd take meter gain away during astral and nerf shell kick. Changing astral means she's no longer a point character and you have to battery for her. The reason Morrigan is so dominant is because she controls meter so well even as a point character. Everyone has a Morrigan counter but if it requires more than 2 meters to do I basically stop listening; you'll basically never have 3 meters against her just because of how the game plays out. If astral no longer builds meter then she's fair at the start of the round and you'd actually have to make a tough choice about how to use her. It's important not to overnerf her because other things that she benefits from like TAC infinites/TAC glitches would be the first things to go in any balance patch and low damage characters benefit from TAC disproportionately. As is her damage on any given hit is 400k+(0.66 x remainder) which puts her damage just too high.
Viper doesn't need a huge nerf either, I think she's reasonable outside of EX seismo. Just make that somewhat more reasonable and she's basically fine.
Other stuff I'd change involve Vergil swords. Spiral swords should be a level 2 with free switches to blistering or crown. A big part of what makes Vergil overpowered is that he's a walking DHC glitch. Low damage characters even as far down as Strider can get big damage off a DHC into Vergil. Between that and taking RT glitch away he's fine.
There's no easy answer to nerfing missiles. Doom as a point character is decent and his value is in TAC infinite and assist so changing foot dive basically returns him to vanilla status where he was only OK. I'd leave foot dive in and just overhaul how missiles work with half of them "getting lost" after he gets hit. I'd change Frank around. The character needs a serious nerf. Level 4 Frank is either too strong or too easy to get to. 1 hit with Nova/Skrull/Vergil or 1 TAC basically guarantees you a monster character without many natural enemies. Either increase the EXP to get to 4 up to 100 or something or make paddlesaws different. Proper paddlesaw use turns about 35 out of 50 characters into completely free wins including some top tier characters. Something's gotta go.
Other characters only need minor things. Wesker needs rhino charge back but shouldn't be overbuffed. He loses to missiles and the engine as much as anything, he's basically the canary in the coal mine for seeing how strong zoning is. Spencer is fine as is even if I hate the character. Dante and Strider are dominant assists and strong characters but don't need anything 1 way or the other. Keeping Strider damage low is good; if he did more damage he'd be Phoenix except with a dominant assist and nobody wants that. Magneto's mostly fine. Removing TAC infinites is an indirect nerf. If anything I'd nerf magnetic blast a little bit by making it not +10000000000 on block. Nothing major though, he's another canary in the coal mine character who should mostly have the game change around him.
Characters need to drop in slightly higher. Task/Skrull and Firebrand/Skrull stuff shouldn't be in the game. Having characters coming in a little higher would give more characters the ability to come in like Phoenix where because of her size Skrull can't get her every time. Characters at least deserve some kind of option to not be completely wiped out on incoming. It would indirectly nerf Viper a little also which is good. Other characters just need small things. Arthur needs gold armor to not be a "please kill me" debuff. He's a dominant anchor character with a decent assist, he could get out of control real fast. She Hulk needs her slide back. Tron needs jump H back.Storm needs her zoning tools improved, with lightning sphere and vertical typhoons needing a speedup. Sentinel needs higher health and a faster fly. X-23 needs dirt nap to advance scaling much further than 1 hit. Nova needs his air throw range reduced and his low M sped up. Joe needs to have red boomerangs go away faster. Give him something better in return like a better slide, but the US is lucky that their best Joe player doesn't practice this game because that character is pretty dumb. Other than that I don't know enough about other characters to know what they need or I don't have a strong opinion one way or the other.