I didnt say that there are no monsters, I said our monsters dont give a good enough risk reward to play. Cannons are excellent against lone characters without Los(cold one cowboys, disc lords, peg heros etc), chariots, other warmachines, monsterous cav/inf/beasts and if worst comes to worst "10 from the back of the general" as 3 cannons will reliably kill him over the course of a game. In addition to that there are monsters that offer a reward worth the risk, Stardragons, hellpits, greater daemons, daemon princes(woc), Terrorghiest make the short list.
Depressingly you will still be hit 55% of the time even if the cannon has no bonuses or rerolls. Hey, at least its better than 66% if you face it so you can charge, right?