Geth has better offensive power? Like yes, that TK on Luke was kinda ridiculous, but sorcery generally is. Talzin actually has the raw power that we don't see from Geth, some crazy lightning feats, and like you said, Immuno-bubble.
What defenses would Geth have if Talzin simply whaps out her Trump card in the form of: http://youtu.be/Se5DuhNdWN0?t=4m36s
I mean, Talzin has some nice raw power, sure. Not sure how that correlates to offensive power though. Her lightning was hastily beaten back by Sidious', at which point she resorted to her barrier. She doesn't really have an offence to compete or a defence against Geth's TK.
Trump card?.. Droid killing lightning, and a blaster bolt stopping shield, is Talzin's trump card? Not seeing it personally. The disparity in their power is pretty drastic when you look at how Talzin dealt with under a dozen droids, compared to what Gethrezion did with a flick of her finger against one hundred stormtroopers.
Well, her barrier can block Lightning, we know that. Her Lightning also carved through those droids, with literally no effort on her part.
And she was levitating herself at the same time looking all BAMFY and shit.
Hastily beaten back is a strong statement. We don't know how long it truly took, but it was enough time for Dooku to recover from force Drain, rise, gather power, and start shooting Lightning. Also enough time for Maul to beat Grevious. Nothing Hasty about that to be honest.