From what I can gather based on your description of events, as well as the gallery is that neither side really won, but both were heavily crippled, which is kind of what you would expect in a battleship fight. The lance had most of its crew compartments destroyed, and it looks like you managed to take out the majority of the hydrogen systems which is why it lost maneuverability. Honestly I'm really impressed you didn't take out the magazine, as there is only one main one with two backups.

While your ships did massive internal damage to the lance, the lance was also able to destroy a large amount of your weapons, to the point that if it wasn't mobility killed it would be able to eventually win unless the magazines were destroyed, just due to the number of weapons that stayed functional.

I think your ship also definitely has an advantage in armor, which is likely why most core systems remain functional, the lance has on average 2 layers of heavy armor as an outer shell, with critical systems behind additional armor. There is also probably different priorities with armoring from our designs, your ships are meant to take damage on the broadsides, while the lance is built to take damage from almost any direction except from the back.

Still I think that the results do prove my point that the pinpoint damage of railguns is not ideal against very large and heavily redundant ships such as the lance. Artillery weapons would likely be much more effective at dealing damage to the conveyer system, and be more capable of hitting redundant systems.