It is true that some ARFs turn out tail heavy. I think this is due to some of them getting heavier balsa in the tail as opposed to the prototypes.

It is also true that some modelers tend to use too much glue on the tail or change out some of the components for stronger, heavier ones.

No matter which one is correct, you have a tail heavy model that needs fixing.
-First, move the battery as far forward as you can get it. In the tank compartment under or beside the tank is best.
-Second, try a brass heavy hub on your AX.
-Third, use a plastic prop instead of a wood one. they weigh more.
-Fourth, check for anything you may have added extra to the tail and remove it.
-Fifth, if you have heavy pushrods, you might want to change to pull-pull cables on your rudder.
-Finally, add some weight to the nose.