Something is not right with Mazian getting trashed by Onslaught in sim or that it needs to stay at range.
No matter how many times I tried it against an onslaught in 1 on 1, all I had to do is literally jam the Mazian into broadside range and exchange sides every few seconds or so and the Mazian will basically curb stomp the Onslaught everytime in the sim.
That onslaught just ate a Blast hammer artillery shell in the face, I love the Blast hammer as on top of being a gargantuan shell... it attract point defense fire and gives my missile better chance of going through as well.
I did angle it so that the natural spread of the shots mean the armor takes more distributed damage across the length
And I did time my Rendfire SRM missile so that it only fires AFTER the Onslaught flak burst finished to avoid wasting having my missiles fly straight into flak cloud.
but otherwise... it's literally just a 'get close', 'sit' and 'spank with broadside', switching sides every few seconds till the other ship kick the bucket under the barrage of gunfire and artillery shells.
I had 1 Mag battery on the rear turret but honestly I would've replaced that with a second Bonecrusher battery if I could... unfortunately I only have 1 of it so I had to make do.
Lost a bit of armor on the bow, mainly on the approach, and a bit on side that took a bit more share than the other one but otherwise finished off the Onslaught with still enough armor to be in fighting condition and no hull loss.
Now to be fair, my captain does have a truck load of skills and in this playthrough of mine, I have the mod to increase the captain's normal level cap limit...
That said, a number of those skills doesn't exactly change the outcome of a 1 on 1 brawl fight against an Onslaught in the face.
The ship carry basically combinations of Magelan weapon (Blast hammer, Bonecrusher battery, Rendfire SRM), normal game weapon (heavy machine guns) and the flak from the Dassault-Mikoyan mod primarily because I can't stomach the look of the normal flak guns.
And for the defensive hull mods I have the Reinforced bulkheads, and Blast door (I looked at the bonus from heavy armor and I don't think I can justify the cost) as well as the exotic mod for maximum armor (at the cost of being more vulnerable to EMP and less durable weapon and engine).
The whole fight sometimes takes less than a minute...