You are correct that they are filled with showboating. But at the same time they very often trigger changes in both policy and public opinion.
If nothing else, they allow us to see that a particular issue is on the radar in Washington, and not just something a bunch of randos on the internet are barking about.
There are hundreds, even thousands, of hearings like this that are productive. The difference is that they're handled more quietly, and are relegated to CSPAN, not HN.
I don't have the perspective to evaluate this claim though. I don't know much about the intersection of politics and media in the 80s and 90s. It seems worth considering though. The premise seems straight forward: broadcasting politicians changes how politicians behave.