Tested some ships the last few weeks. Galaxy/D10/KBOP fly pretty good, yet are not invicible. No balance issues as far as Im concerned. I am a little less sure about ACR and Defiant. ACR flies easy as well, yet may get in to trouble easily when multiple enemies are around. It appears to be harder to fight with a Defiant, mostly due to new ship specs from other ships. I dont think they are imbalanced: not all ships have to be easy. Im not sure about the D7 either, but that is mostly due to its similarities with D10 and D11. For my kind of flying, D10 and D11 apperar to be a better choice.
Didnt try excel and Keldon yet.