I use cannons simply because I always have in my empire armies, back through to when empire armies first appeared. I don't like too much 'higher' fantasy stuff, like the demigryphs, for aesthetic reasons. Decisions regarding what to include, for me, are not that often about what gives the best competitive edge, as other factors affect my thinking, usually story or theme, or the urge to aim for a 'lower' fantasy.
In my Tilean campaign, for example, I see the 'standard' NPC state army, the little army they keep around as a core to which stuff, like mercenaries, can be added to bulk them up in a time if emergency, as some foot (melee and missile), some horse (light or heavy) and a cannon. Characters kept on the army pay roll would be a fighting captain and an artillerist (engineer) to tend the 'arsenal'. Which is why the above 'in game' photo came about - five allied armies, 2 players and 3 NPCs, all brought a canon or two and an engineer. That was some battery. The opposition player lost all his monsters in turn one, and quit the hobby for good! His action might seem understandable, but what he had failed to take into account was that while he had already had success after success in his battles, picking off foes one by one, or ill-prepared alliance armies, a certain player had struggled politically for several game seasons (and the best part of two years in the real world) to create that alliance army and get it operating against the enemy. The crazy number of cannons and engineers had happened as an unexpected consequence of my thinking concerning what the standard practice would be for little, standing armies.
To be honest, it boils down to the different sort of thinking that goes into campaign, story-focused armies, rather than tournament style game-competitive armies. I have some players who think that way, and they are welcome to do so, to make for challenging realms in the campaign. But I myself just got caught up in the world(s) and hadn't given any thought to the 'Cannons = Crutch' issue until the incident with the allied armies and the player taking his bat home!