Ah I see what you are saying. I was thinking in terms of modern navy ships, and thinking of using higher tech engines for battletech versions of them. They still don't get quite as light as that engine, but the higher tech ones do make the ratios a lot closer. Also I have to point out that the wiki article on it does give the weight of the main engine, but the propeller shaft also has five more diesel generators, and 2 electric motors powering it. It has a steam turbine that takes a lot of the engine's exhaust and recycles it into more power as well, along with associated electric motors.
Also, Battletech as far as I understand it, would also be including the weight of the propellers and all the other machinery working to propel the ship forward in it's abstract "Engine weight", which would account for some of the disparity.
That fuel efficiency difference sucks though. I have no explanation for that.
A C tech rating Fuel Cell engine that goes 3-5 would be 8736 tons, and the fuel for that 34,725.6, with a super charger adding another 873.6 tons. That is much closer tot he other's engine weight, though even that is ten times the weight.
In terms of modern navy ships, my biggest beef with the current rules is the how they determine the available space. You can remake WWII ships alright, but recreating 21st century ships becomes more difficult because you have the tonnage, but lack the space to recreate them.