In "Is electricity instantaneous?" there were several answers that differentiate between 'electron flow' and 'current flow': electrons move slowly through a conductor, but the resulting current moves near the speed of light.
Given: 1 Coulomb = "6.3 billion electrons passing one point in a circuit in one second" [noted that this is not reflected in the SI definition which is 'the constant current needed to produce a (given) force in parallel conductors...']. Most sources I have read go with the "electrons/sec" definition, or "charge/sec" definition - including the tag here for electric-current. As a chemist I equate "charge" with "electrons" (not 'current flow').
Question: is a Coulomb based on a 'count' of slow electrons, or on the fast electric field generated by the moving electrons? [acknowledging that as a derived unit the Coulomb is really based on the Ampere - but this seems to be kind of circular reasoning at some level]