Darth Sidious did the same thing on Byss, with 16 billion people who didn't even realise it was happening, he did this slowly, with his own power and no rituals, whilst basically on vacation relaxing in his armchair, he also managed to mindwipe the entire of Coruscant so they didn't remember a Super Star Destroyer being parked underneath the Imperial Palace.
I totally agree that in a full scale battle of empires, the Galactic Empire would win. I just question whether Sidious could really be more powerful than a guy who consumed the power of all the individuals in his home planet (N-something?). Besides, lightsaber combat between two Sith Sorcerers (I think they'd both fall under that category) is pretty pointless. It'd be a contest of will and force power.
Oh and Darth Sidious was an ambidextrous master of every lightsaber form whilst Vitiate is noted as being no combatant at all and relatively useless with a lightsaber in the Revan novel.