I hear you man, Like I said, yesterday was an 8.44 lb'er for me and it was only 177 after 17 hours in a steady 275 pit. It doesn't seem to add up at all.
I'd rule out 1 and 2. I don't think a bit of twine compacting it, nor the rub layer would have an impact beyond the first hour or so. If I had to guess on the science behind it - probably has a lot to do with things like humidity levels, atmospheric pressure, air circulation in the cooker, and the composition/age of the individual piece of meat. All things out of our control as pitmasters.
I really think it's just the nature of the beast. I remember on the first one I couldn't believe everything I read on the site re: taking 2 hours or more per pound. It cruised right through the stall period without hesitation. It wasn't until I experienced such a dramatically loooong cook yesterday that it hit home.
By the same token, I've read about everyone cooking their big packer briskets for 18 hours or even longer at 225-250 chamber temp. My brother in law did a 13.5 pound packer a couple weeks back and had that sucker to 209 in 7 hours running 200-225 in his vertical propane smoker. He foiled after 4 hours and at the 7 hour point it was falling apart to the point of almost not being slice-able, 209 internal temp according to an accurate probe thermometer. According to everything I've read, it should be flat out impossible to get it done that fast at those temps, but I witnessed it with my own eyes (and thermometer) the entire way.
The only explanation I can find is that elevation may have something to do with it. My pork picnic that was done in 9 hours, and that packer brisket done in 7 hours, were both cooked at the same house way up in the NH mountains. The pork butt I did yesterday that took forever was right at sea level. Maybe that has something to do with it?