Exactly. Harrow is on his own, just out to protect Jimmy's son. He's Travis Bickle at that point. A disaffected, detached from reality war vet with a stockpile of weapons and high level killing skills. They even do the shot from Taxi Driver where he's laying out his arsenal.
I thought the scenes with Gretchen Moll and Cannavale were the best either has done all year.