Nor was I attempting giving a fully general counterargument against all Fermi calculations
You may not have been attempting to make a fully general counterargument, but you did in fact make an argument against Fermi calculations, without referring to any specific Fermi calculation, that fails to distinguish between good Fermi calculations and bad Fermi calculations.
You may not have been attempting to make a fully general counterargument, but you did in fact make an argument against Fermi calculations, without referring to any specific Fermi calculation, that fails to distinguish between good Fermi calculations and bad Fermi calculations.