To summarize
The pursuit of the whale took over 1 hour. The harpoon was finally fired but hit the whale in the lower abdomen and the whale was not killed. It took 11 minutes before the first rifle shot was fired at the whale in an attempt to kill it. Six more rifle shots were fired in the next three minutes as the men on board struggled to winch the whale to the side of the boat. The harpoon appeared to have passed right through the lower abdomen, tearing a massive hole in the whale's body from which the intestines were protruding. As far as we can tell from the footage, the whale died at least 14 minutes and 28 seconds after the impact of the harpoon, although it may have been alive much longer.
In my opinion, the captain of this crew should lose his license. I don't know if this has happened, or will.
Such accidents are rare. It was documented in 2002, when every whaling boat had an inspector with a stop watch on board, that 80% of the animals die within seconds. That said, the fact that these things occur is a valid argument against whaling - unlike, in my opinion, any of the other considerations you have presented, which seem to me red herrings.
It is not enough to make me change my position, though, given that unacceptable accidents occur in all hunting, and even in all slaughter. Thousands of chickens were boiled alive in an accident last year; I personally still eat chicken. Hopefully, standards will continue to improve in both departments, making such incidents more and more infrequent, although it's unrealistic to expect them to never occur. The world's northernmost desert wind.
