I don't think deadliness of the round was ever in question. It was a question of stopping power. The 45 ACP came about because the .38 was not stopping Moro warriors in the PI. There was a Doctor involved with the cartridge testing back then who wrote a book, LaGarde was his name I believe, and I somehow manage to get a copy years ago.
The Moros are still causing trouble today with kidnappings in the southern PI. The Spanish had mucho problems with the Moros and the Spanish only had control of fortified towns, mostly ports, in the southern islands. Stepping outside the walls was not a safe thing to do for the Spanish. When the US took over the PI, we ended up fighting a war with the Moros which was unpopular in the US but we did win and shutdown the Moro terror, raids, and piracy. The Moros were very brave and it took quite a bit to stop them. They would attack with a bolo and decapitate people and the existing rounds were not stopping the up close attacks.
Later,
Dan