Little things could still be tweaked a little. Velocities of cannon and muskets for this period tended to be higher when the shot leaves the gun than what we have on the projectiles file as the projectile velocity. If we adjust the velocities upwards a little, with a few more tweaks cannons would kill a bit more.
The problem is that the AI uses cannons badly and then cannons used by the human player risk becoming a bit of an exploit. That was part of the reason why they were made so expensive. There is one situation, however, when cannons can be used with great effect, despite their other disadvantages.
"Many a Burger in this City, coming forth in his holy-dayes clothes to take the ayre, went never home againe till he was carried quicke or dead, where from had their heads separated from their bodies by the Cannon; as happened to one Lieutenant and thirteen Souldiers that had their fourteene heads shot from them by one Cannon bullet at once"
Robert Monro, His Expedition. Part I, the 16th Observation