Cannon feels more like a sniper: pinpoint accuracy, infinite range, small explosion, and, most important of all, low visibility to enemies as it's the only way in the game to assume prone position, ergo players aren't used to looking for people in prone.
I got a game with 100+ frags but it wasn't >fun< because I'm just sitting there, almost invisible, clicking on enemies one by one.
Maybe increase the visibility of the cannon while increasing it's explosive range?
On the other hand it may simply be a skill issue of a playerbase full of new players, idk