“1. Undergunned. 12 gauge is a great tool for aggressive humans. It ain’t enough for aggressive black bears. “
By all accounts a 12 G w slugs is plenty for a black bear, and is even acceptable for Griz at close range. The failure in this case was due to poor marksmanship. A hit in the same spot from a 375 H&H would likely have the same result. Not following up on the wounded bear was unforgivable.
As Colonel Cooper used to say, a hit with a .22 short is better than a loud miss with a .44 Mag.
More Range Time appears to be indicated here.