I don't think that more prims will solve the problem because the heaviest core can't even support those 4. I agree that noob dreadnoughts will win over noob battleships and that they are capable of dominating the battlefield if simply forced forward together, like we've seen in Magellan. A skilled captain with a light BS will mostly kill a skilled heavy BS, though.
I am against the "fat = dead" motto, so I am not exactly sure of what should be done. I think that the current stats are balanced, but I think that what was proposed here is balanced too. It gives heavy battleships an even greater advantage from close, but as their guns have a shorter range than conventional BS prims, an even greater disadvantage at long range.
I think that this is interesting, but I also think that what is not broken should not be fixed. That is why I am not sure.