20+ year concert shooter here. Sometimes you just have to use flash. Shitty dark punk rock venue with some random Home Depot lights? Flash. Esp with punk rock and awesome slow shutter effects. Performance during event with flat lighting with flash allowed in the venue? Flash. Most other gigs? No flash. It’s a tool, horses for courses.
Tbh - way better to know how to use a flash effectively in all occasions and not needing it is better than having no clue/inflexible values (“it’s not true to the ART!!!”) and having to turn in useable shots at the end of the show.
Paid.