Willing to make MN BB6 to compete in Harbour tiles, just forget it. Seriously, I'll say you've chosen a wrong nation if you want something that stand a chance in a bb6 especially in line fight.
If you want to compete in bb6 line fight, the doors are open for any other nation. It's mean to say that, but that's the truth.
It took me a KM bb6 grind to fully understand, that KM in general, isn't made for GB and so I start over with UK for doing well in GB.
Let's face it, charlemagne won't be able to compete in line fight. Some ship shines in BB room, some in GB room.
Kaiser is usefull in HA, but is crap compared to QV in GB. QV is usefull in GB , but is crap compared to Amagi, Nebby, and kaiser.
To balance is another thing,but to make it competing against other bb6 especially on linefight forget it.
Plus, it's not a linefighter to begin with.