when i started university the first degree i ended up studying for was a music degree (i was vastly underqualified so i switched) and man, the amount of guys there who were so technically proficient and absolute theory wizzes... who could not write an effective pop song to save their lives. christ.
they were polite guys! they'd play lovely songs for us all during lunch! but in your feedback you'd have to focus as much as you could on complimenting their playing because you could never be so impolite as to say that the bit where they dipped into 13/8 for two bars was in service of nothing.
if you did say something, it'd be a bit like *that* bit from Spinal Tap. "why didn't you just stay in 6/8 and play something really resonant and memorable for that specific two bar phrase, and then you wouldn't have to go into 13/8 just to shake things up" ".... but we went into 13/8". etc.