According to his experience with killers, the most important thing to ensure is that they don't touch him. This step has only become more important since Sword Mastero's Supreme Metac will definitely injure him regardless of the power of his defensive means.
Even though his external body had cut off any means of ranged attacks from Sword Mastero, Loki wasn't satisfied. He wanted to make himself untraceable. That way Sword Mastero won't be able to hit him.
As for the Thousand Cuts Metac, it was to increase the lethality of the Devouring Ability. The job of the Thousand Cuts Metac was to increase his attack speed. It does this job by multiplying the injuries he inflicts on a target.
So the Thousand Cuts doesn't actually increase the power of his attacks. It only helps him pile on damage faster by turning one hit into a thousand hits. Of course, this will cost him a thousand times more energy to use.
