I got the exact opposite impression, actually: I thought it was about finding hope

I guess it's an indication of the narrative working in one way or another if people can watch it and draw completely opposite messages from it. : )

I really do think "Numero Cinco" is the key to the entire season, although what I got was something more like Angel eventually found a way to "take heart," if you could call it that, in the fact that his heart is "a dried up piece of gnarly beef jerky" - he can do things by not having the heart of a hero that those with a stronger sense of moral convinction (e.g., Lorne) cannot. I found that message kinda grim... and a traged for Angel, that eventually he had to find his comfort in his usefulness as a monster, not a man.