[annnnd]

Actually, your experience sounds great! In general, it is much easier to find people with narrow interests. While it might seem to you that you are not employable, this is just an illusion - there are many developers, but few with experience "from development to product design to finance". This makes you a great fit for virtually any smaller company which doesn't have a separate person for each role - startups, new businesses,...

TL;DR: You didn't fail. You learned.

As for burnout - been there. If it's any consolation, it will go away once you find something new that will keep you motivated.