Ship Challenges 2.0 is Broken (Really)

It’s definitely true that ships 2.0 has made getting your tarkin to 5* a lot harder. Most of this, though, I think is due to tarkin’s ultimate no longer being a game ending wipe. It used to be that you just needed to have your ships survive long enough for the ultimate, and if you had just a fraction of health left on your tie fighter (which also used to dodge more) at ultimate time, you could kill like all 5 enemies as long as they only had about half their health left. Also, Phoenix ships got a huge boost with 2.0 which makes the opponents starting line a lot tougher. And without any good tanks, DS really struggles to kill that starting lineup before all your attackers are dead.
Only advice I could give you is keep trying, maybe start gearing your Bossk now and once HT hits shipments upgrade it to 4* so you can use it on the challenge (if you haven’t beat it by then). But fleets do require a lot of resources, so you’re going to have to choose between gearing your pilots, or your arena team. That’s why you see a lot of empire teams around your level, because they’re the only ones that can do both (Vader, Tarkin and even TFP do well under EP at your level). Good luck.