Oh so you have a Bottom tier as well... that probably makes more sense.
The thing with tiers in MvC3 is unlike previous games, the gap between top/middle/low tier is very small. There are some very obvious top tier characters, then a massive middle tier, and a small obvious low tier that does still shine even against the top tier from time to time (Arthur vs Phoenix). Technically, once you get Wolverine, Phoenix, and Wesker out of the way the path is pretty wide for who follows and how closely.
I know that but even with the basic definition of a Mid/Low character... someone who is Low would have to be at least worse than half of the characters in the game or more. Someone like X-23 is better than at least 15-20 characters in the game and thus should not be considered LOW tier AT ALL.
I would say that both Felicia and X-23 are upper mid.
Haggar is mid tier and better than people give him credit for, even on point. Chun-Li/Hsien-Ko/Arthur are bottom tier and far below low tier.
My low tier is something like Iron Man/Chris/Felicia/Capt/Thor/Morrigan. These guys have their saving points unlike the bottom tier.
Iron Man is NOT low tier and neither is Chris... wtf. I wanna see your entire tier list because I think we are at a disparity as to what we both consider a "mid" character in the game.
I will post mine for posterity.
S TIER (aka TOP tier)
Phoenix, Wolverine, Dante, Wesker, Magneto, Zero, Viper, Amaterasu
A TIER (aka HIGH/NEAR TOP tier)
Spencer, She Hulk, Taskmaster, Trish, Akuma, Dormammu, Doom
B TIER ( aka UPPER MID tier)
Storm, Sentinel, Tron, Iron Man, X-23, Felicia, Spider Man, Deadpool
C TIER (aka MID tier)
Ryu, Chris, Thor, Super Skrull, Jill, MODOK, Hulk, Haggar
D TIER (aka LOWER MID tier)
Viewtiful Joe, Morrigan, Captain America, Shuma Gorath
E/F TIER (aka Worst tier)
Hsien Ko, Arthur, Chun Li
I will even give explanation as to what a tier entails for me.
S tier is obvious... best of the best. In order to be S tier the bare minimum qualification is that the character has to be at an equal competitive level with those other characters without the use of assists. These characters excel at tools at their disposal, mix ups, damage, priority etc.
A tier are characters who basically scratch at the heels of the S tier in that they will defeat them no sweat on a given day but they will probably require an assist or two to come up at their level. A few of the A tiers are there on the strength of their assist being absurdly good like Akuma.
B tier are characters who require considerable work to be at the level of A tier. They have the tools and damage but execution requirement and just being outperformed by S tier in similar categories put them here but they have superior match ups against the latter half of the game. Tron and Sentinel are there because their assists are top and some of these characters are there due to DHC glitch.
C tier characters are the average joes. Basically if they touch you they will make it hurt and you can't sleep on them and some of them have the tools but they are also held back by genuine weaknesses or some execution requirement. They basically have something not everything... they will either have lots of damage/health but low mobility mix ups or they will have mobility/mix ups but will either lack damage or have high execution requirement just to be at A/B level.
D tier characters even if you get past their execution barrier they don't deliver the same punch as even some of the C tiers not to mention bad normals, bad throw game and bad mobility. These characters also struggle to pick up opponents after a hard knockdown even with the help of assists which over time has proven to be a helpful attribute in dishing out quick and easy damage.
E/F tier or whatever you want to call it are the worst of the worst and they suck at pretty much everything outside of a couple gimmicks that allow them to win a match or two. These 3 characters at the bare minimum have good assists and thus can be put in a team to win a match but once they are on point... you better start praying. Even if you are a robot with these characters, you can't make it hurt without X Factor/ton of meter.