Unless that prop was already on fire or had low health, that flare isn't going to insta-kill someone. Like I said earlier, a flare only does 30 damage without crits. And by the time you can shoot those 5 flares, the shotgun has already shot more than that. Comparing them shot-to-shot doesn't work too well. Heck, comparing two different types of weapons doesn't work well, either.
And don't take anything I say about the shotgun the wrong way. I personally think it's fine as is.
I've also been trying to come up with a solution to perhaps have the reserve shooter not as nerfed. Just haven't had much time (or patience with this cruddy phone) to do some number crunching. That thing does like, at most 10 or 15 damage. And that's with luck it seems.