If the copy becomes distracting in the design then you are doing something wrong or they are discussing copy changes. It might be a bit annoying but you could tell them that that discussion would be best suited. You begin with a text, you sculpt information, you chisel away what’s not needed, you come.

Then the question arises: where’s the content? Not there yet? That’s not so bad, there’s dummy copy to the rescue. But worse, what if the fish doesn’t fit in the can, the foot’s to big for the boot? Or to small? To short sentences, to many headings, images too large for the proposed design, or too small, or they fit in but it looks iffy for reasons the folks in the meeting can’t quite tell right now, but they’re unhappy, somehow. A client that’s unhappy for a reason is a problem, a client that’s unhappy though.