I agree. Karma's performance is a statistical fact. She doesn't have the raw damage and hard CC of other AP champs. Her heal and shield and speed buffs are underpowered compared to everybody. And then she has mana issues and high cooldowns.
I mid Karma quite a bit. Usually successfully, using the Mantra shield, Heavenly Wave combo. The champs I'm having issues with are Morde (can't do enough damage to get past his shield due to cooldowns and mana issues), Akali (she has no mana, huge damage, stealth attacks and escapes, closer, practically non-existent cooldowns), Kat (huge damage, closer/escape, no mana. massive OP ult that Karma can't counter), Lux (range above 1000, hard CC to prevent closing), Ryze (hard CC, and can get damage boost from mana items, that's nice for him). Champs that bring a couple health potions usually mean I run out of mana before I can get their health down, and then they can just walk away since they have hard CC or escapes.
I've tried her as a support, and she's underwhelming. She does little damage with support setups, and has a very underwhelming heal, plus short range.
I'm thinking retooling her W is needed. Having it DAMAGE THE TARGET suddenly makes it useful. Since her Q is such short range, make her W a closer, consuming the spirit bond and moving Karma to the target on a second use, and a escape by allowing it to work on wards and towers. The current speed/slow is not enough to deal with the closers and CC that most champions have. This also allows Karma to be a more effective support as she can sneak up in the bushes to harass and escape when it gets tough. A small range increase would be good too.
Her main attack is her Q, but the cooldown is 6 seconds. Akali cooldowns at level 5: Q:4, E:3, R:1. So Akali Rs in, drops a smoke screen, R's again, Qs, Es, Rs again... then stands around safe in her smoke while her Q and E reset. Karma can Q, R, E... then stand around like a tool getting hammered. So I think a change to her Q cooldown is justified. Or maybe nerf Akali? I dunno. Your call, Riot. Oh, and Akali's Essence of Shadow has a lower cooldown than Karma's Mantra... That's nice for her.
I find her passive to be underwhelming as well. You get stronger right as you become a massive target in a teamfight? Doesn't sound like much of an advantage, especially as all your abilities will likely be on cooldown at this point. I don't really have an alternative I like.
So keep the mana usage and lack of hard CC and two Mantra charges (Akali gets three Essence of Shadow with her shorter cooldown, btw), since we don't want to make Karma OP, like Akali... But give her a third ability that can do damage reliably and a closer/escape to make her competitive and a shorter Q cooldown to make her useful in an extended teamfight. That still let's other mids counter Karma with health potions, as Karma will have mana issues still as a control on her damage.