Speaking of the electronics, most dropships or bigger military vessels are able to generates ECM by themselves, without need for an additional gear.
Since sub-compact warships are capped at 25,000 tons, they are ill suited for anything related with combat. As said above you better have a patrol warship that resembles civilian jumpships. Even the 10,000 tons assault dropships are far better combatant.
Well, at least the lighter weight gives an advantage - it generates less traces when they jumps.
That depends thoroughly on what you're packing in the few weapons bays you've got. If it's energy weapons? you're absolutely right, same for most ballistics that might fit.
but, y'know...strategic mobility plus nuclear ordnance changes things quite a bit, and while you can pack more on a dropship, that dropship can't go anywhere out of the system without a fragile jumpship to carry it, and can't pull in-system jumps on it's own, and CAN be lured into the wrong position to be of any value whatsoever as a defense unit simply by responding to your arrival.
By the time he gets to where he can respond to you for real, you've already accomplished your mission and he's shit out of luck. Pull the local defenders into responding in one direction with the ultralight, and drop your invasion in where they aren't, or conduct your raid where he can't make interception in a reasonable amount of time because he was responding to a light strike bird.
or if he doesn't you can do fun things to his shipyards and other strategic assets, cripple his trade economy, attack his bases...see, you just need some imagination here-in a straight fight, sure, but if you're giving a straight fight you're using it wrong.