Been gone a while are fire sorcs viable now for PVM with sunder?

Is it able to break all immunes with gear now?

If so any links to a decent build?

yup, they're great now.

use a sunder and this build:
6x rbf -30/+xx weapon
flickering flame
viper rbf
phoenix monarch
mages
arach
aldurs/rare boots
+2 sorc/fire 15+ fcr amu
2x fcr rings

you won't even need to spend coins on an infy merc to be effective with all that - enemy res on your gear.
alternate build route is to use a +3 fire 20 fcr double rbf circ and sojs instead of flickering flame + fcr rings