But it wont matter if it cant catch up to the thing its suppose to hit and if they cant get trough point defence. . .
In my current game, my first gen railgun corvette escort ( made with spit, bubblegum and little prayer ) has 2343 km/s speed and eight railguns linked to 12k km/s tracking speed fire control. . . My 8k tons corvette can in theory neutralize entire salvo from your 90k tons dreadnought, almost 100 % of the times. I wouldn't be suprised if group of 11 ( 88k tons - still less than your ship ) of my corvettes could destroy that massive ship of yours just by rushing full speed, swatting your salvos and sandpapering it to death ( especially that your beam weapons aren't some glorious thing either ). 11 corvettes with 8 railguns each ? Thats 352 shots every five seconds - thats your entire ( fully charged !! ) shield and some armour damage in one strike. And with little above 1k km/s speed of your ship, i would have 100% accuracy.
Its just not good design. .
That's no what his design is designed for. Like he mentioned this design is meant for planetary bombardment respectively. It's whole design purpose isn't to duke it out with corvettes or any other smaller craft, the design is meant specifically for planet bombardment (stationary). I assume he has other designs in mind to accompany said ship to deal with other craft trying to intercept it.
I generally don't design ships that are good at everything, from my experience you'll always end up with a ship trying to do everything but isn't good at anything you want it to do. Maybe that's my lack of dedication to do in depth number crunching, but I always go for designs that are good at a specific purpose.
In my current game I have 3 different designs for cruisers who have exactly the same tonnage but with different weapon systems to deal with different threats. I'm not going to send a battlecruiser that's mean for planet bombardment into a swarm of corvettes without ships that are actually meant to deal with it.