Slitherine

I noticed when reading through the manual that although the use of a bayonet can cancel a lot of enemy melee POA, it doesn't seem to give any positive effect against enemies without bayonet.

This can give an odd situation where bayonet armed troops have no advantage against a pure bow/musket formation.

Was this done intentionally, and if so what are the historical/gameplay reasons for this? I thought that if a musket+bayonet would be long enough to deter cavalry it should at least act as a kind of spear with similar effects in melee.

In this period most bayonets were of the plug variety that went into the musket barrel. It was primarily a defence against cavalry and would be unlikely to be fixed against infantry, because fixing it prevented the musket from being fired.

Overall, it was sufficiently inefficient that giving a close combat bonus for it seemed inappropriate.

Ah, that makes sense. I was thinking about the Napoleonic image of the bayonet charge, so that would be the socket bayonet type.