Just finished a playthrough with the Alastair as a primary flagship so here are a couple thoughts.
The Alastair is by far the weakest out of all the other battlecruiser / battleships of the game. I would even go so far as to say that some heavy crusiers with the right angle and speed can beat the Alastair if they are able to maintain a flank angle during the fight. The reason is that they have 4 back facing turrets (2 of them mediums) and another 2 side turrets. That means there's a possiblity of 5-6 turrets not firing if a ship takes a minor side angle against the Alastair in a ship to ship engagement. For reference most ships battleships / battlecrusiers have at most only have 2 SMALL back facing turrets for PD. On top of that, the Alastair's main guns are also latched on as side turrets, meaning it too might also not be firing. Due to the reasons stated above, the most common thing I've noticed the Alastair doing is contantly turning and turning to get at least 50% of the turrets firing during any engagement. Therefore, the Alastair CANNOT be used with high pressure auto firing weapons. It simply needs to turn too much. Because of the awkward turret angles, it results in poor distance management and can be run down or out ran accordingly.
The most success I've had with the Alastair is as an artillery platform + mini carrier with lots of PD.
As you can tell, I had more grievances with this ship despite how awesome the Alastair looks. So here are some thoughts on how to make this ship a bit more viable:
-Bump its ordiance up from 285 to 300. A Legion Battlecarrier has 285 but has 4 fighter slots.
-Give it another fighter bay. Right now there's no point in specializing a carrier build because it only benefits 2 squadrons.
-Make those 2 bastard Medium turrets facing backwards turn at least 270 if not 360. The Command deck should not prevent the turret from firing over it.
-Consider buffing the built in Siege Cannon. It does next to nothing.
I spent over 30 hours with this ship. I wish it could be better. The Lightinning attack is super cool. Never get tired of seeing that.