Tecnically I don't think there are bad ships. Depending on your playstyle you just have to find the right ship for you and if you fly another you have to adapt to it to make it work.
Obviously the Excelsior is the sweetspot for a lot of people cruiserwise.
It does decent damage because of it's high tactical ability mostly.
I am not sure why you survive longer in the Excelsior then in the Sovereign, must have something to do with your defense value.
For me the sweet spot is the Sovereign.
It is so smack in the middle of playstyles, to me it feels like it can do everything.
My setup is "as tanky as needed, as deadly as still possible".
However I would still call her a supportship.
I can wear other players down and even win against multiple ships, as ker'rat is proving again and again lately.
But my Achilles heal are sci CC builds.
I can't do squat against them. If they disable me I am space dust.
And when escorts do the smart thing (and run) before I destroy them I have nothing to prevent them from it.
Well except the graviton console I got from a gold box.
But what I really need to squeeze into there would be a tractor beam but that would only be possible with an Odyssey...