Bobby Short played the Carlyle Hotel for 3 or 4 decades with just his voice and a grand piano, and if you weren't rich or famous, you couldn't get in the place. I don't think he worried too much about staying current with the music either. I'm just saying, arrangers are fun (for short periods) but are certainly not essential for a singles (OMB) gig. Being talented and a true professional helps. JMO.

chas