In a similar vein, horse archers cannot be killed by any infantry except archer/longbowmen and gunpowder units.It's just impossible that horse archers would sit still and let spearmen strab them.
Speaking of horse archers, they should be very interesting with the extra moves & ranged bombardment!![]()
Yes, unless the spearmen managed to surround all 6 hexes of the horse archer. Then he would be toast.

The disparity between ranged units and melee units will be pretty extreme. Historically, archery was far more difficult to learn than basic melee combat (horseback archery being even more insanely difficult). I hope this will be reflected in the units' relative training time/costs.
Even muskets were inferior to longbows in that era. The big advantage muskets had was that they were much simpler and easier to use than longbows (typical longbows used in warfare had draw weights exceeding 150lbs!!!). Thus it was much faster and infinitely more feasible to build an army of musketmen than it ever was for longbowmen.