Yeah that always seemed like an unfair characterization of the DS9 set to me. Just because the TNG set was so supremely
silly, and people were constantly joking and clowning around, doesn't mean everyone else was doing something wrong. It's likely the DS9 cast simply took their jobs a bit more seriously, is all.
And it's not like there isn't plenty of behind the scenes footage of the DS9 cast (Brooks included) laughing and joking around with each other as well.