This is meant for fleet protection and given the range of TL9 jump-capable construction is 100-4000, 400dtons is pretty big.
Basically its a Screening and Range Extention Role. I want to point out the following: Sensor Model-9, Accel 5.5, and Armor of 70 (high in TL9).
It is really meant to screen for information, extending to the farthest range of the fleet its protecting. Maybe extending a very deep protection scheme of 3 layers (Scan-22 x 3). Prevent anyone from threating the heavier ships CRs, BBs, and Carriers.
Given their speed they can actually almost keep up with some Fighters, still its role is conservative and defensive. Against what the imperium can dish out in TL10, the destroyers are capable of being a match against the picket fleets of the imperium.
DD squadron (2 DD, 2DDH, 4DDL)
Light Destroyers are 200dtons, Heavy Destroyers are 600dtons. I'll come by with more stats later on. That and I have to come up with stats for Cruisers.
Disclaimer: the spreadsheet tool I made is pretty much my tinkering so sorry in advance for the inaccuracies. I will update all my work and put date stamps so that you know if it incorporates the newest corrections. I realize I can easily gloss over some data because of staring at the spreadsheets too long.
TL9 400 Dton Destroyer
Tech Level: 9
Hull: 400-dton Stealthed Streamlined Cylinder hull, dDR 70 armor.
Systems: 51 Maneuver Drive, Standard Bridge, Model-9 Sensors (Scan 22), 80 Fuel Tanks (Capable of 2 Jumps-1), 16 Staterooms, 4 Bunkrooms, 15 Vehicle Bays (15 Life Pods), 5 Light Turret, 13 Beam Lasers /TL9, 2 Missile Racks, 141 Fission Power Plants, Cargo 6-1/2.
Statistics: Emass 1721 tons, Lmass 1947 tons, Cost M $1,400, SM +9, Asig +4, Hull dHP 60, 62 Life Support, sAccel 5.5 G, Jump-1 Capability (2 Jumps), Top Air Speed 540 mph.
Crew: Command Section (3 officer, 1 Petty officer), Flight Command Section Flight (1 officer, 1 Crewman), Enginering (4 officer, 8 Petty officer, 28 Crew), Gunnery ( 1 officer, 2 Petty officer, 3 Crew), Maintenance ( 1 officer, 1 Petty officer), Life Support ( 1 officer, 1 Petty officer), General Service ( 1 officer, 1 Petty officer, 1 Crew), Medical (1 Petty Officer). Total 11 Officers, 15 Petty officers, 33 Crewmen.