They were subject to counter-battery fire.
Allies usually have lot better artillery, except Chinese.
Thus, I wish AI Japanese would not use that unless superior, they just suffer losses and enemy gains experience.
In general, having longer ranged or heavier artillery is an advantage in artillery duels. The Japanese have a limited amount of very heavy artillery - up to 350 mm (13.8") but they tend to use that at the point of their deepest thrust, or against the most fortified bases. The US 155mm M1918 GPF, 155mm M1A1, and 155mm Long Tom seem to be very good at counter battery fire because of their range and accuracy.
Thus I wish AI would be bit "smarter" in use of artillery..alas..it is what it is.
Bombardment is very useful in situation where you have artillery superiority but not evough AV to assault.
"To meaningless French Idealism, Liberty, Fraternity and Equality...we answer with German Realism, Infantry, Cavalry and Artillery" -Prince von Bülov, 1870-