Am I bad at the Game or is Asura Ara extremely squishy?

I started 2 days ago again after a really long time and tried out Dark Knight first and had trouble at the Besma map (I know, pathetic) After that I thought I try Ara and wrecked almost everything(except Altera, fuck those nasods) up to Peita Map and loved it. But ever since I reached Belden I absolutely got my Ass handed to me from bosses and get 3 to 4 shotted from bosses and chug poitions like Mountain Dew. I am lvl 58 and have equipped the best equipment I found and still I feel pretty squishy. After some frustrating maps of revive and pain I jumped back to Dark Knight again and all the troubles I had are gone, even Altera was a joke to beat. And now I’m wondering. Is Asura weak or am I really bad at the game or did I just need some warm up Phase with the game why I had trouble with Dark Knight and now I have none. Thanks for the answers in advance :3

PS: is there a way to get the class costumes for ever and not just a couple days?