Well, we don't know when the Barbette (i.e. a 'fat' turret) gets introduced. So early PB may require a single barbette instead of eventually getting down to being two-per-turret.
Not to overly complicate things, but a PA, with it's radiation damage, seems like a purely military weapon to me. And navies and such would most likely be loathe to let any Zad, Dorn, or Harry run around the galaxy with them if they could somehow make it a little harder (like say you need a warrant or something from a planet or even pay a fee to the Imperium for authorization to have one) for ordinary people to have heavy weapons like this.
So maybe it would be the proper place to introduce the heavy laser, with close to the power (consumption and damage) of a PA, but none of the radiation damage. It would also allow you to scale the PA properly TL wise, and have the heavy laser introduced one TL after beam/pulse. Then you could take the PA out of the CRB since it's really a purely offensive weapon. A heavy laser is, too, but it's really more of a big brother to the other lasers. I dunno if you'd wanna split it into heavy pulse, and heavy beam, or just keep it as a heavy laser period.