The only way to make the Bristlehead a crow is to lump woodswallows, Batis, bush-shrikes, Vangas, drongos, fantails, monarch flycatchers, and shrikes as crows. At that point, Corvidae is rendered so heterogeneous that it loses any context of meaning for most birders.
Yes! And ioras, birds of paradise, orioles, vireos, painted berrypeckers - shove them all in! This would make Corvidae heterogenous to an approximately similar degree as traditionally defined Anatidae, Psittacidae, Phasianidae, Accipitridae and so on. All of those corvoid groups would still represent recognisable units to birders, regardless of their formal, familial designation...
...and this still does not explain why 'family' doesn't consistently indicate a more or less certain degree of divergence across all avian orders. I think I've figured out the answer now anyway. Simply, there is a stronger resistance to lumping traditionally circumscribed families than there is to creating new ones - regardless of the level of genuine divergence. Therefore, when it turns out that traditional members of a particular family (e.g.
Cettia) are closer to members of a different traditional family (Aegithalidae) than they are to other members of their own traditional family (Sylviidae) - the preferred result is to split them into multiple families rather than including them in a family with their closer relatives, or, lumping all together. This seems to be regardless of whether or not the level of genetic or morphological divergence is roughly equivalent to that of a subfamily, a tribe or even a genus. A driving factor behind this seems to be the fact that passerines are so speciose.
Mysticete, it was enjoyable discussing this with you even if our opinions are at odds. Certainly, we can both look forward to the future designation of Pachycaridae, Oreoscopidae, Ifritidae, Rhagologidae, Eulacestomidae, Platylophidae, Melampittidae, Hemipidae, Chaetorhynchidae, Lamproliidae, Namibornidae, Geomaliidae, Cataponeridae, Auriparidae, Cephalopyridae, Maliidae, Micromacronidae, Carpospizidae, Amaurocichlidae, Sporopipidae, Amblyospizidae, Icteriidae, Zeledoniidae, Mitrospingidae, Lamprospizidae and Saltatoridae |=)|