It seems like late game is all about massing siege engines.
Mangonels melt infantry.
Cannons melt castles and in mass do well against most units.
Mass springs are kinda are effective vs cannons if you have enough and decent choke points.
A few stout units in front to soak damage.
So a siege unit to counter everything else, and with their range and high damage, can make up the bulk of your army? Unless you have a map with narrow choke points, even mass springs could get overrun by cannons.