^^Ditto^^ Ablative paint should wear from the outside in. If the paint is flaking in large chips all the way down to fiberglass, then it is an issue with the paint properly bonding to the hull. Painting over it will not help as it is the base that is loosing the bond. When this occurs the old paint releases from the hull along with the new paint on top of it. The newly painted areas continue to chip for the same reason the previous layers chipped.
This is due to hull preparation prior to the first coat of paint being applied. It could be residual wax, residual bond release from the factory, or the hull was not properly or completely sanded in that area, or the area was not completely cleaned of gelcoat dust between the sanding and the application of bottom paint. And finally, a barrier coat of proper thickness prior to painting will not only help prevent water intrusion, but also aid in the paint in bonding. If you were to apply a barrier coat, you would need to completely strip the hull down to fiberglass.
I had the bottom of my boat soda blasted. I then applied a couple of coats of barrier coat, then a couple of coats of bottom paint.