Yep, it's not actually "instincts" more like "intuition" or "clairvoyant intuition".
However, in the LN, Lewin's instincts don't tell him his comrades are dead, rather the "instinct" is limited to avoiding immediate, great danger. Mangaka probably changed that to speed the story up a little.
"Darkness of evil" sure mate. believe darkness being evil when you did slaughter so many innocent people... it would mean your light is pure evil. more evil than darkness. hmm.