If you judge a fish by its ability to climb a tree, its going to live its life thinking its a failure.
If you judge the SSD by its ability to defeat A) the starhawk, a ship designed specifically to counter rogue SSDs or B) a entire fleet by itself when the full power Executor was taken down by a equivelant force to most 400pt fleets, then i think your barking up the wrong tree.
As with every quite literally every other ship, fleet, upgrade, etc in armada, there are situations it is great in and situations it is screwed.
For example a bomber list. I would rate the SSD highly here as it can take the gear to punish fighters and wipe out the ships.
Against lots of capital ships? If its by itself its going to have to take all the shots, which unlike the fighters will be boosted by upgrades such as x17s, critical effects, etc.
Theres always going to be the unfavourable matchups, unfortunately armada is in the position where these unfavourable situations for the SSD are commonplace to deal with other high hull, high shield beast ships (ISD, super pickle, mc75, etc)
And i feel like ive rambled without getting to the point
sorry lol
My point? The SSD is actually quite well balanced, but the competitive meta is currently at a point where taking down large ships is easy enough if they are the largest point sink/threat. And guess what the SSD currently is.