There are demographic trends though. Millennials are a lot more likely to be the product of helicopter parents which makes them very bad at asserting themselves, it also gives them higher expectations on where they’ll start, and much weaker problem solving skills. I’ve got friends in HR and some of their millennial stories are scary, like their parents calling in to negotiate salary, and refute performance reviews. Is that all millennials? No of course not. Is it most? No. Is it a higher percentage than Xers and Boomers? Yes. And that’s where knowing your demographics comes in. Each group is different, much like you wouldn’t bring in spicy burritos for a team lunch if the team is made up primary of very midwestern white people. Know the trends for who surrounds.
I'll add that it's both demographic and cultural. A sizeable portion of the "Millenials" I deal with come from immigrant families -- where the challenges you often find with the children of American-born parents usually don't exist.
If one doesn’t know the people, one can ask the question.
Demographics are statistical in nature - true for the broad brush, but liable to be completely false for the individual.
Demographics are also the handmaiden of identity politics (which translates to other arenas due to categorization errors).
For example, I am a very midwestern white person and would dearly love spicy burritos for lunch! LOL
In my line of work, that would be immediate grounds for dismissal. I have to be correct (that is, I have to have a strong, technical reason for my opinion), and I have to be assertive about my correctness. If I am ever incorrect, I have to be gracious in admitting it.
If I had an employee unable to defend their position, they would not be an employee for long (assuming they ever got past the initial interview).
I understand what you are saying, and I tailor my speech patterns to the likely experience of my audience (such as not mentioning old TV Shows to younger folks, etc.). But I cannot foresee viably making decisions based on demographic assumptions.
You present your case well, BTW, although I do not agree with it.