Skirmish negated by fliers?
 

It seems that skirmishers ability to prevent counter attacks (except against other skirmishers) is negated by the existence of fliers? This makes fliers significantly more valuable, in my book.

Any feedback on whether this is indeed how the game works?

Archers and Fliers do assist with defense even if the unit attacked by the skirmisher doesn't attack. Fliers are really useful for killing weakened fleeing troops. They seem more useful then light cavalry which gets killed quicker.