I need schooling - old vs. new engines

I have a Blueprint Engines 408 in my '70 Duster (w/Quick Fuel 750 VS) that runs great yet has a choppy idle. I also have a 2021 Challenger with a 392. The Challenger has more advertised HP & torque yet has a dead smooth idle and gets ~ 23MPG if I'm easy on it.

Besides the fuel injection being more efficient, why would the newer engine be so "tame" while delivering such smooth power on acceleration? Thanks guys.