I don't have an issue with the large number of fire controls; expensive to build but it's one method of confounding point defence and may save a fortune in ordnance if you need it. It may be excessive against most targets you're likely to face and there are more elegant methods of achieving it, but the principle is sound.
For beam PD, something similar applies. You go out of your way to defend against many small missile salvos... but the details are worth questioning. Your impressive Gauss tech doesn't do you much good if you spend so much money on expensive fire controls. On a fast ship like the Defender, 10cm railguns would get the job done as efficiently, for less resources, and with better firepower in a brawl if that becomes an issue.
Armour seems excessive, I'd rather invest more in active defences.
Last but not least, your propulsion plants are too stressed, which is imo the easiest way to ruin a design.
If I understand it correctly, the Defender uses 100HS of fuel and 70HS of engines.
3 maximum size engines with power multiplier of 1.3 and 20HS fuel fits into the same space. You get better range and speed on 1/5 of the fuel use.
