Kind of a banal observation. Every study is inherently flawed because one can never fully isolate a system, can't go back in time to repeat the experiment under identical circumstances, can't measure precisely what you want to measure because of uncertainty or circumstance, etc, etc, etc.

Knowledge production is very hard, very incremental. It is a messy, human, endeavor, even in the hardest of sciences. It is fine, even virtuous, to point out its limitations, but glib dismissals can sometimes just be a cognitive stop or rhetorical device.