I just recorded a band whose timing was all over the place with each other but they were happy with the playing.
I would think it's usually one guy that's really off and maybe pulling the others.
You need to
diplomatically demonstrate the problem without appearing like you are picking on anyone and explain the potential issues of going forward without addressing it....
...then yeah, if they want to shrug it off, at least there is no chance they can toss it back at you, like you should have said something.
But lots of people are intimidated in the studio even if they are normally solid players when they gig.
So, someone has to run the show, and often that’s either the engineer or the producer or both, unless there is a strong leader in the band (not an ego-tripper) who understands the whole process.
But you really can't expect too much forward thinking from a band that's green in the studio.
You are part of the process...so take pride in your work and not just the money. I don’t like that “the customer is always right” approach when everyone is making creative decisions, but only some have the technical skill to understand how to make them happen.
While I don’t do a lot of outside work…whenever I’ve recorded others, I always felt and wanted to be a part of the project, and not just a knob jockey…so yeah, if it sounds like shit…I’m going to say something.