I don't think kelborn is overpowered maybe Cadeus and I think Zannah is fine

Zannah-She's definitely a tough nut to crack but she does very little else. At 1/4 or more of your squad she's not always worth it.
LS,GH-I don't really consider him broken at all. Could you explain this one a bit more?
Darth Caedus-Probably the closest to broken here. Caedus is nasty. But that's all he is-nasty. His SBM is very good, and he's a decent beat, but that's it.
Kelborn-With a base 10 I don't think he's really broken. Even if he is the Mandos need it.

My opinion is that:
- there was massive power creep in the Wizards sets between 2004-2007, as the game evolved from a casual game to a competitive game. Some factions got better and better, while others didn't get much love from Wizards at all.
- since around Legacy of the Force, powercreep has levelled out a lot - there's just a little, to make the meta change each set, and this hasn't really changed since we transitioned from Wizards to v-sets. It seems like a bunch of pieces are getting added to the competitive meta each set, without too much falling out the other end that was already good. It seems more like an expansion, than old pieces constantly being burned off - a lot of pieces that were good in 2008 are still good (like Captain Rex and the Lancer).
- the handful of problematic pieces in the v-sets (imo the biggest culprits are Geonosian Drones and the Naboo stuff, but I have seen other people make arguments for Mace, Lord Kaan, and Bastila as well - in any case, these pieces have all been well and truly argued over already) is concentrated in the first couple of sets. I think the last 3 sets have been fine, and I can't think of anything I have a problem with.

In terms of the pieces you mentioned, most of them are in factions that needed some help - I'd regard them more as power balancing than power creep. Specifically:
- Darth Zannah - to be honest, I don't like seeing her on the other end of the table - she's actually one of my least favourite pieces to play against as on her day she can take a long time to whittle down. But I think objectively she's about right for her cost - she's hard to kill, but doesn't do much damage either. GOWK is much worse IMO - he has an awesome Commander Effect, and he's in a faction that's stronger overall.
- Caedus, Sith Lord - he's really good for the points, but Sith needed something else good at the top tables rather than just Revan all the time.
- Luke Skywalker, Galactic Hero - I like him, I haven't seen any squads with him that are dominant yet. Seems fairly priced to me, and I certainly wouldn't pick him out as overpowered.
- Kelborn - he's amazing for 28 points, but in a faction that really needed help.

At LowerHuttACon recently, we had 18 squads. Noone ran Kelborn, but the one Luke GH squad came in 12th, the Caedus squads came in 15th and 16th, and the Zannah squad came in 17th.

That's true, interesting.

Indeed the Drones can be a huge problem with the sheer volume of them that can be crammed into a squad and beefed, haven't seen to much Naboo so I can't comment.

She has a meager 40 damage output, and can only do it on the move if she spends a Force point (bad idea, since she needs those Force points for Bubble and rerolls). FC3 is nice but there's no way I'm giving up 3FP for rerolls/Bubble.

If your opponent's squad attacks her then the rest of your squad is good, and it they attack your other figures than she can use corruption. And usually by the time she fights she has around 5 fp. Even more with either DFS.

Sorry but all of the above regarding Zannah is right. The bubbles and rerolls are too important to lose to be able to use corruprtion. she is hard to hit yes but if she gets based she is probably in trouble. also her damage output is extremely lacking and there isn't to many (cheap) ways to boost it.

They don't have to choose one plan of action. They can attack her, switch to someone else until she uss Corruption, then take advantage of her low Force points to hit her.

Yep. Even with her tank-iness, someting like Mace will still take her down quick 1v1.