First shooting is not really a problem due to shield regeneration. Check some different setups and you will see that it matters more which shield breaks first which depends on formation and setup.
If you have equal numbers then losses are dramatic indeed. With bigger and more diverse fleets the losses are spread out more.
You can be active as defender and use self support. With self support you will have an advantage as defender as you can influence the match-up. I think it is fine that defenders which are not active have a small disadvantage.
Yes. It is a game and it is not realistic but we need to simplify it as no one can manage 3D fights with multiple ships in a web browser.
Happy to hear your constructive improvement suggestions that are realistic to implement. (Unfortunately we will not be able to implement 3D fights in virtual realty. ;-)
RE: Battle mechanics in detail