Ok, after some quick testing:

First of all, DAMN the controlls are bad/retarded. You just seem to notice it much more when you play with only 1-2 units. And DAMN the battle AI is stupid, even more evident when you play against 1-2 units.

Anyway, test showed that 1 unit of men at arms combined with 1 unit of retinue longbowmen did did come out better than using 2 units of armoured wordsmen against 1 unit of JHI.

However, mainly thanks to the computers love of the tactic "rush in, withdraw, and stand around and look stupid as you are peppered with arrows".

So in this very controlled setting, yes indeed longbows were worth it.

HOWEVER, you are not commonly attacked by JHI, but rather troops with shields and first and foremost mounted troops (knights).

And that's the main problem, knights (and their muslim counterpart) are just too fast so you dont get many volleys off.

My problem still stands, I see little or no reason to bring archers along except 1 unit for morale issues.