You should consider transferring over to a Mage because in my personal playthrough in terraria, Mage helped me all the way to the final boss. You should use (or collect) Mage gear on some of the lower tier bosses to get used to it, then slowly get to higher difficulty bosses till you're a full fledged Mage. (this is just a suggestion) good luck with your fight!!!
For the weapon against the destroyer...hm. Try to get that upgraded repeater...I don't remember the name I will recommend the name when I search it. And build a platform way up in the sky. There is a limit to how high he can fly (works for me). He would stay below me and shoot lasers at me while I shoot my Gatling gun at him. Good luck