Agree that soot is pretty common with straight blowback actions, but it doesn't happen all the time. It's very ammunition dependent.
That FPC woodlotowner saw must have had aftermarket BUIS mounted, and I'm not surprised that they didn't work well. No fault of the rifle, the FPC design really does demand an optic. Sure, most people probably prefer using a red dot on both, but the S2K doesn't force you to. If the iron sights don't work for you, that's too bad. But they work for lots of people.
I don't know how anyone can say the FPC packs better than the S2K. While they're both really close in length, the FPC is significantly worse in every other way that matters: heavier, thicker, taller. And when folded, the S2K is far, far more packable.
Fit and finish, sure, the FPC probably seems nicer to most people, but not everybody cares much about that. I'm more interested to see how the design holds up in the long term, and what kind of warranty support S&W has for it. The S2K was a truly ingenious design and has proven itself. The FPC is a not-so-original copy, with some strange design choices (buttstock, LOP, grip length, bolt release, safety location etc.).
I'm glad we have options. I strongly recommend anyone in the market to check them out in person and see for themselves.