I understand it's not easy. At no point did I say it was easy. But let's look at the numbers here.
According to the Wikipedia article on the incident, 300 law enforcement officers responded to the TAC alert issued. Over 600 rounds were fired at Emil Matasareanu and Larry Phillips, Jr, during the conflict. The two men themselves fired around 1,000 rounds at police. While I understand mentioning that I got these figures from Wikipedia cheapens my argument, all of them have an in line citation with a source. 19 officers received the LAPD's Medal of Valor for their actions during the shootout.
Now, knowing this, we can assume that at least 19 officers were directly engaged with the gunmen during the firefight, which lasted 44 minutes. The incident occurred in a suburban part of Los Angeles, and like most of LA, this area was made up of a grid of streets. The bank faced a parking lot, separated by a boulevard. Behind the parking lot was a professional building.
I understand that the officers were equipped with Beretta 92 model pistols and 12 gauge shotguns. It might have been a long shot, but if you could have hidden at least some of those 19 officers in that professional building and spread them throughout the building, you would have made it much harder for the two robbers to pick out their targets, and would have made a much less stressed shot for the officers. The distance would have also made the shot harder for the suspects, whom were more of the spray and pray discipline.
Another thing to consider is that the bank was flanked by two parking lots, both of which are relatively wide. Another place to make a surprise, somewhat timed shot on the suspects. Drive a police car (with its sirens off... at this point in the shooting, it would be obvious that you don't want to draw attention to yourself as being a LEO) on angle with the building across the lot, pull your pistol out, fire. A shotgun might have a certain level of effectiveness here as well, because the energy exerted through the body armor might cause blunt force trauma.
There were definitely enough officers involved to have taken the men out earlier than they did, even with the weapons provided.
Overall, at least in hindsight, the main problem was poor tactics. I probably couldn't have done better myself, but who's to say better training and aim wouldn't help?
As a final note, I find it incredibly ironic that the LAPD went to a local gun store to get a hold of weapons capable of penetrating the body armor of the men. Really ironic. If the SWAT team hadn't arrived in time, the patrol officers would have had to borrow guns from the very people they were regulating.
Back to subject, I suppose...
