Huge fan of Rak Gol, and although it pertains little to the BFG/ship combat aspect of it I heartily recommend checking out The Koronus Bestiary for more info on them as a race.
Like Jimmy (sup buddy?) I am actually pretty happy with your interpretation, as it seems really fitting. If you want my 75 bucks worth though:
1) Is there any additional way to represent the absurdly high shot content of rak'gol howler cannons? I mean, they literally fire twice as many shots as other macro-batteries, albeit at roughly half strength. What if they always counted all armor values as one point higher (to a maximum of 6), but increased their battery value by roughly 50%? Or is that just too plain foolish of a thought? Basically they would be less accurate per shot but get a lot more to compensate.
2) No one said Rak'Gol lances are not good, just that like everything else they create it is stupidly inefficient for what it does. That said, you are right that lances are not the end all of their tech and that they should be more reliant on boarding, h&r and howler cannons for offence.
3) What if they had an ability similar to the Chaos pdf from GW for Khorne vessels. Basically they get to add +1d3 attack craft to a wave but cannot launch ordnance next turn...sort of like a big alpha strike swarm of boarding madness. Could make it like the howler cannon suggestion and make it a stat change: their launch bays are 50% bigger, but can only launch craft once every other turn, no matter what. Powerful but inneficient.
Just thoughts, try not to be offended if I sound like a cheap hooker in a run down casino in Reno with a bad case of the shakes. Just trying to incorporate my enthusiasm.