Not sure I'd go quite that far, but we've become so accustomed to electronic ignition & fuel injection and how little maintenance modern vehicles require that we forget how performance falls off almost imperceptibly on older cars after a few thousand miles. Do a tune up and/or carb rebuild and WOW! what a difference.
Undeniably, the slant (or at least the 225...never driven one of the smaller ones) was a peppy engine, especially compared to the Ford 6's (170/200) of that era. My first car was a Falcon with a 144...what a slug!
