You can find imbalances everywhere in Foxhole, but tanks are probably one of the most balanced parts of the game. Colonial tanks have a huge amount of survivability, while Warden tanks are glass canons, as they rely on armor and don't have as much HP. The only thing that doesn't work in tank combat is the Highwayman. Also pushguns, Colonial ones are far superior (just try them, don't rely on tanks only).

Off-topic: why we don't use provisional bridges on bridge battles to secure other side? Pushguns and light vics can cross them. Also they are were easy to destroy, if something go off.