.... why can I delete the ballast and run battery voltage to the coil of a pertronixs ignitor 2 w/ matching coil, but not a mopar performance ignition with non-factory coil ? ...
The Pertronix Ignitor II is similar to the GM HEI ECU. It has smart electronics to manage the coil current. Their Ignitor III is even better having multi-spark (MSD's namesake) and a rev limiter (I recall).
Earlier after-market ignitions were more like the Mopar ECU, i.e. mostly just a single transistor w/o smarts. All those need a ballast. That includes the original Ignitor, Crane Cams XR700 (XR3000 was a race-only "no ballast" version, both originally by Allison), and probably early Mallory, MP, etc.