It seems clear that the police were under attack and fired upon by someone with significant training and pretty powerful weapons. Your argument that the fact the assault wasn't stopped by cops in ordinary cruisers indicates we can't prove the armored vehicles saved lives is just ridiculous.
Have there been any where police were shot? Perhaps you recall this one...
https://en.wikipedia.org/wiki/North_Hollywood_shootout
No military vehicles, 11 cops and 7 civilians shot. Cops had to commandeer an armored car to evacuate the wounded because 2 guys had them pinned down. They were unable to do anything against superior fire power despite having significantly outnumbered the perpetrators.
Is the number police killed or wounded too low to justify having armored vehicles to protect them? Should we tell the spouses and children of police officers that cops can't have unarmed armored vehicles or as some mistakenly call them "tanks" because not enough cops die in shootouts to justify the added protection? Your arguments are getting better and better.