But why would the difference between populism/democracy even be a useful distinction to make if both served the interests of "the commom man" equally?

One measure of a functioning democracy is how it approaches compromise between differing opinions and respecting the rights of those who don't agree with you. Actively pitting one group against another works against this. It can easily lead to what's known as the tyranny of the majority: https://en.wikipedia.org/wiki/Tyranny_of_the_majority

On the other hand some people are worried about the rise of a ruling elite centralized in government, media, and universities, with a partial influence and cooperation of the military industry. The deep state.

This group of decision-makers would like the public to think they operate on behalf of the interest of the state and act on the basis of "scientific principles".

Arguing that this is essentialy social control and that this constitutes the basis of the "tyranny of the elite" may not be flawed.

There's always the need of a balance between extreme tendencies. The liberal premise that the political elite has the right and obligation to make fundamental decisions on behalf of the mass of citizens has its limits.

and everyone is some kind of minority in some way or another. This is why solidarity is so critical.