Consortium 5 hero raid
First off, this idea is not based on experience, I'm mostly speculating.
The consortium has 5 cloaked heroes. This gives them the ability to attack any planet straight on the ground with 5 heroes (and an unlimited number of defilers...). If we use common sense and say that 5 heroes will defeat 5 normal ground units, this means that a player can waste the whole pop cap a planet gives (5) on protecting that planet, since he can be attacked anywhere anytime. Additionally, the ZC even has acces to Orbital Bombardement (!) when attacking a planet with a cloaked Tyber, since the Merciless gives that advantage even without winning the space battle.
Silri's pet makes any tower defence obsolete.
Also, the fact that the Merciless is cloaked allows e.g. the following scenario:
A rebel or Empire player leaves a space station level 1 or 2 or a small fleet undefended. The ZC player spends a minimal amount of credits to bribe e.g. 2 starviper squads to that system (to start a space battle) and proceeds to own the enemy fleet with a cap ship hero.
IMO this is not really what one would call balanced...
My suggestion would be to make Silri, Tyber and possibly Urai Fen normal,i.e. non-cloaked hereos:
Tyber to prevent the "cloaked cap ship owns enemy fleet" scenario as well as the "raid with orbital bombardent" phenomen.
Silri, because her rancor is just a too powerful unit to be deployable anywhere and owns any tower defence, which could be used to fend off other "hero raids"
Urai Fen simply because he too is extremly powerful with cloaking and regenaritive abilities and is extremly hard to fend off for an unprepared Force since he can just hide and regenarate.
I know that the Rebel raid can be quite powerful too, however this is one of the Rebels' main advantages that the ZC should perhaps not get in an enhanced form...