This thing has always been trash tier in terms of performance though it does have the cool factor of many guns, too bad they spend the battle endlessly spinning and chasing everything on the field instead of actually shooting their guns at good targets, what's more is how often they're out classed by much cheaper ships. Onslaught can barley 1v1 a Radiant but Dominator, Aurora, Fury, Afflictor, Doom can all do this with very little issue and they are all cheaper.
I've tried just about every meta build that's been posted and it's consistently worse than a Prometheus MK 2, Odyssey, Conquest, It can't chase the things it can kill and is outpaced by phase skimmer, Dominator will catch and kill that fleeing Radiant without having to push it to the top. Dominator will also kill Brilliants and Novas quicker. So it can't kill smaller ships in reasonable time and can barley fight Radiants despite smaller ships managing it and it's distracted by ships that can't even scratch the paint and don't have the firepower to turn its engine off.
Give it an Eliminate order with an Aggressive pilot and watch it ignore that order to endlessly swing its TPCs trying to shoot frigates that are harassing this is what I mean by laughably bad. As a player you literally ignore those frigates and they will die to autofiring PD and crossing your main guns you can't tell the AI to ignore which is a massive oversight. So there it goes endlessly spinning.
Give it an Escort and watch the Escort block its guns and then retreat path leaving the Onslaught, you guessed it spinning in confusion.
Missiles, 4 Med missile mounts, let's spend 40OP on reapers, 30 more to EMR, and we've spent 70 points for missles that get dodged, eaten by PD, or lobbed at max range at a frigate. What a deal that is, so leave them empty, oh now it's been given an Eliminate order up north but it's heading south chasing a frigate even though my other frigates are also chasing their frigates. The AI has too much option, it must be lobotomized, the Onslaught is literally built to point at target, press F, hold click and WIN but it cannot do it, I don't know why it can't do it. I can do it. You can do it, AI simple cannot do it.
Anyway it was entertaining watching how awful this ship still is compared to the rest of the Capitals, as for fixing it idk double it's range remove the TPCs maybe it will be half as good as a Dominator. Until then its back to the Conquest and Oddy combo, speed + range = win by default.
An anagram for Onslaught is Tons Laugh as in I laughed tons at just how poor the ship is.