You must leave and keep looking until the right line up appears. I tried auditioning for several bands and didnt think much cop of any of them. In the end I auditioned and formed my own band (although now its our band and all decisions are taken democratically which isnt hard as there's only 3 of us!) My point is you will Never Be Happy with this guy, he will not improve very much at this point in his "developement" and you will be forever frustrated. Be polite but firm with the other bandmembers and say it's me or him, if it's you then so be it, move on, another opportunity will come along, I promise!