Taking this seriously for a moment here, you'd be screwed on any bosses with a high amount of Force/Tech attacks, as your damage reduction will be half that of a shadow, already the weakest tank against those types of attacks. You'd also lack any sort of true defensive cooldowns, meaning you've got nothing for "oh ****" situations. And without a taunt, you cannot perform any sort of a tank swap and will have huge issues with bosses that drop aggro.
All that being said... I bet geared this way, you could probably tank HM EV. You'd have to force your DPS to give you a 10 second headstart to make sure you maintain aggro tho. Actually... Annhilator droid has a threat drop, I forgot, so yeah, maybe not.
You could do most of the hard mode flashpoints tho.
Err... this isa bit off subject.
But man what game you playing? Shadowtanks have the best mitigation of force/tech attacks of the three tanking classes. If you are kinetic damage, than yes the shadow is weaker. But over all because of the self healing abilities shadow has greater surviavability than jedi guardian.