I'm curious why you say this?.... The Bolt has the first one, and the Volt has the second. And they're apparently different enough to ....
And how can you explain the difference in plain english?
Again, the only layman's way I know of testing this subject is to stop using the Brake pedal in D with the regen display at or near the max. Them hop out and measure brake disc temps with an IR reader.
The results will probably be the same on both of these GM EV's.