Nobody is assuming anything. If a bear does charge you at 35mph at short range you're probably toast anyway unless you're sitting in something armor plated weighing at least a few tons. I'm pretty sure most people could hit a moving target with bear spray a lot more consistently than with a firearm, though.

The same goes for incapacitating yourself. It seems to me a lot of people who have reservations about bear spray have never tested it before. I'm not saying it's a be all, end all solution but it does have a very good track effort considering the circumstances. With just a little bit of training I believe most people could use bear spray more effectively in an emergency than a firearm. Other than that, there aren't that many decent options left. Things like axes, knives or flares really belong into the last ditch category IMHO. YMMV.