I'm gonna defend the conquest here. It's much fast than an onslaught at 45 base speed instead of 25, and while burn drive is faster in a straight line I would say maneuvering thrusters is better overall due to its versatility.
But you already knew that.
What the conquest doesn't get enough credit for is its DISSIPATION. Its base dissipation is twice that of the onslaught, full stop. 1200 vs 600. Even slapping on 50 vents only nets you 500 dissipation, so this difference is massive.
This lets the conquest field flux hungry weapons like the gauss cannon much easier, while also having enough agility that you can't pin it down. AND it has 2 large missile slots, which is the best weapon type in the game as far as I can tell.
Something you should consider doing is stacking up ballistic mastery and gunnery implants with your gauss cannon, then adding unstable injectors. The range of your weapons drops from 2220 to 1887, which still outranges almost anything, but that 15 speed brings you up to 60 which is comparable to cruisers BEFORE you use maneuvering thrusters. Grab coordinated maneuvers and slap some officers into a couple monitors and you can easily max out your nav rating. With max CR and helmsmanship this adds up to a 40% speed boost, plus another flat 5 for the elite effect of helmsmanship.
83 speed. On a ship with 1887 range kinetics and 2 hurricanes. And it has maneuvering thrusters.
The conquest is really good in its niche, but you're never going to see the AI bring out that potential. The AI is much better at handling a straightforward battleship like the onslaught than it is a battlecruiser, even if it's a really good one.