  Flat spectrum radio quasars (FSRQs) and BL Lacs are powerful jet producing
active galactic nuclei associated with supermassive black holes accreting at
high and low Eddington rates, respectively. Based on the Millennium Simulation,
Gardner and Done (2014; 2018) have predicted their redshift distribution by
appealing to ideas from the spin paradigm in a way that exposes a need for a
deeper discussion on three interrelated issues: (1) an overprediction of BL
Lacs compared to flat spectrum radio quasars; (2) a difference in FSRQ and BL
Lac distributions; (3) a need for powerful but different jets at separated
cosmic times. Beginning with Gardner and Done's determination of Fermi
observable FSRQs based on the distribution of thermal accretion across cosmic
time from the Millennium Simulation, we connect FSRQs to BL Lacs by way of the
gap paradigm for black hole accretion and jet formation to address the above
issues in a unified way. We identify a physical constraint in the paradigm for
the numbers of BL Lacs that naturally leads to separate peaks in time for
different albeit powerful jets. In addition, we both identify as puzzling and
ascribe physical significance to a tail end in the BL Lac curve versus redshift
that is unseen in the redshift distribution for FSRQs.
