5 years or not is irrelevant - the guy clearly has no idea how to dial-in / eq his tones -or- quite possibly his hearing isn't that great anymore -> this is a serious and growing problem in society generally [ regardless of digital amp modelling ] put down almost exclusively to the habitual / almost "24/7" use of in-ear-buds at "louder always sounds better volumes". Also he could just want to be louder because he is "audio selfish" / just wants to be "the loudest" because the world needs to "hear him play" ...... these guys really do exist.
I'd just tell him to turn down / refuse to play with him if he persists.
I really feel for your singer
Either way, the rigs being used have nothing to do with the situation.
Ben