Generally speaking even in legacy content it can be to your benefit to bring more people. When farming old content for whatever drop you are after you double your chances of acquiring it for every extra person you bring.
So while “not required” is true, “it is beneficial to be grouped” is also still true.
When my wife and I find a drop from old content that we want, we go at it together because we can trade said drop to the one of us that wants it.