Dont apologise for the long post; it shows how much you thought about the issue.

I find loose formation can actually be quite good at helping crappy units absorb a charge, because the gaps and enemy tight formation minimise the charge attacks they make.

The distinction I make between archer-spearmen and all other archers is that they can handle light and medium cavalry well. Numidian Archers with their clubs aren't going to do so well against cavalry. That's what distinguishes archer-spearmen from the other light archers, even those light archers that carry a decent secondary.
I actually did a quick little test, facing Numidians and Arabians against Germanic Light and Cappadocian Medium cavalry, and found the Numidians to actually be better than the Arabians (the Arabians couldnt beat the mediums where the Numidians did, though that may have been due to general kills against the Arabs). Obviously, this superiority only applies to Indian/Ethiopian/Numidian archers, but nonetheless I still am not moved to seperate out archer-spearmen in my own estimation.

Also, 'bad archers' do not have inferior morale to most 'good archers' (both mostly have 8-9/low); the main problem there is the smaller unit size. But I dont dispute that they're pretty crappy either way.