That video explains a lot about what happened. A few key points like, the captain was concerned with using all retardant to it's maximum effectiveness. This had two results, 1 he pulled out of the first drop to save some retardant for a second go on a more favorable line, and 2, once on that line he was very concerned with ensuring the retardant 'tagged' or continued to first drop for maximum effect. That then gets anyone in the mindset of fixating on the second drop point to ensure it's all worthwhile. The fixation is evident when the pilot bunts the nose down late in the approach probably to follow the target in the windscreen and that small change in such a large aircraft resulted in a combination of very low thrust and high rate of descent. Everything is out of whack now and in what would be a normal recovery is now low, and with a full spool up required for any performance, by the time you realize what has happened you are flicking the hilltop.
I can see a few ways to reduce it happening again. PM needs to be drilled on watching all parameters, IAS and ALT are obvious, but power and attitude and descent rate as well, what would be called stable approach criteria. Set drop points to overlap, and not tag, yes you waste a little bit of retardant, but if you start to miss you are less likely to push the nose down subconsciously (or just can tagging and drop the retardant without target restraints). Also given the response time of the engines would it be better to have these aircraft fitted with modified spoilers so that they can use significant power against drag, if performance is required, ditching the spoilers with 80%+ N1 would be much faster response than spooling from idle, but then I supposed the cowboy operators would use them to dive bomb canyons or something....