I'm certainly no expert on the matter. I've only killed 2 grizzlies in my life, but with 45 straight years of living, hunting and photographing wildlife in Alaska, I've had at least my fair share of bear encounters. (And shopping trips to Cy's in Kodiak). I lived in Kodiak 1987-1991. Hunted there since 1980.
In Alaska, I believe a large percentage of the bears shot in defense of "life or property", did not need to be shot. It's really pretty rare that a bear encounter is of the close range, full-on charge that comes without warning. In fact, most bears really don't demonstrate aggressiveness at all.
The one that did charge hard at me did so because I was sitting beside a creek, fleshing a wolf hide that I had just shot. I'm sure the bear thought I was an injured wolf and didn't want me to get away. It met the working end of my .375 H&H at 30 yards.
The ones I've had try to intimidate me generally pressed forward towards me with head down but laser focused. They don't always come on a straight line towards you and will sit and watch you briefly. I've had them stomp with their front feet and huff at me or pop their jaws and drool.
I have not yet encountered a bear that was so close and so aggressive that I haven't had time to unsling a rifle and be ready. When not packing my rifle, my 10mm is in a chest holster and fast to draw as is my bear spray. I believe the spray will be effective most of the time in the encounters that I'VE had. But, I always want to be armed with a gun. But my untrained opinion is that 95 percent of bears don't want any part of us, about 4 percent will try to intimidate us and 1 percent will actually try to kill us.
I'm sure that we are all in more danger from drunk driver's or driver's texting than actually being attacked, let alone killed, by a bear.