BALLAST RESISTOR........WHAT GIVES?

Yes, the HEI is internally current limited to about 5.5 amps. Problem is that this is more than the Mopar & other ballast resistor coils are designed to work with & run hot without external current limiting with the risk of failing from overheating.
The ign coil current sees the HEI, Pertronix, points etc as just an on/off switch. The coil neither cares, nor knows, what is doing the switching.
If the coil was designed to use a bal res, it should be used with the HEI.
The HEI was designed to use a coil with low primary resistance [ 0.6 ohm ] which provided a high current spark [ the heat in the current is what ignites the mixture, more current more heat ]. A great coil to use with HEI is the MSD 8207 E core coil, no bal res reqd, 300mA.