I think the difference between L1 and L2 is much more the than most people would guess. I am working on doing a comparison study but don't have very accurate numbers yet. One thing I noticed was that the Bolt L1 cable uses 16 gauge wire while my 2013 LEAFs L1 used 12 gauge. I calculated the Chevy L1 would use 15 watts more in cable loss at 12 amp charging. My present estimate for the charging efficency is as follows:
Measured from breaker box to DC into battery on the Bolt, 12A Chevy L1, 7.2KW L2:
Admittedly, one big factor is the L2 was installed next to the breaker box to minimize wiring loss and the L1 is coming from an existing 15A outlet on the far end of my garage. I did change the outlet receptacle to a commercial grade one though.
Hopefully, I'll have more accurate data soon.