I believe you are correct, but the real issue was not the firearms the robbers were using, but rather the penetrating power of the police firearms against the robbers' body armor[1]. Because they were both wearing body armor, the two bank robbers were shot a total of 40 times without being killed. (One shot himself and the other bled to death).

Police at that point were mostly using 9mm pistols, .38 caliber revolvers, and 12 gauge shotguns, none of which were capable of penetrating the body armor. More heavily armed police such as SWAT were using MP5s, which shot 9mm as well.

The robbery lead to the distribution of higher velocity firearms like the M16 among the LAPD, and a similar incident in Miami lead to the adoption of the 10mm pistol cartridge by thy FBI.

[1] https://web.archive.org/web/20150702091610/http://www.police...