Well good for you! Never let facts or common sense stand in your way
Fact is he's right. A bear can cover ground at more than 40 km per hour if it wants to, and chances are if it's actually a dangerous bear, you won't know or possibly even see it till it's pretty close. You'll have one or two chances to make a shot that will stop the bear.
The fact is - if you actually look at the cases where bears were stopped with guns, (and the bear was hostile and charging, not just a nuisance bear that was destroyed), the vast vast majority of SUCCESSFUL examples involve firing at very close ranges. People that shoot at a bear while it's still a fair ways off (especially a big bear like a griz, not so much black bears) often didn't fair so well.
I honestly believe it's the noise as much as anything that makes them break off - a face full of fire and sound is extremely disorienting and frightening to the bear. Big bears can shrug off amazing damage and keep going, but if they break off to figure out 'what the hell THAT was', then suddenly their systems start to shut down if you've wounded them badly.
I would be practicing to make two or three really good shots rather than hoping you'll get a chance for 8. Unless you're chuck norris and expecting to be attacked by a dozen highly trained ninja-bears at the same time.

Practice dropping to a knee (to get 'level' with the bear so your shots go end-to-end, not just down thru it) and wait till they're closer in (25 yards or less).