I share your alarm at management bull, so can see why you might have switched off.
Yes, some companies use the term sloppily, just the way some firms say 'logistics' instead of 'moving stuff about'. But that doesn't mean some companies don't use it. Principles and standards of getting what customers want, methods of testing and demonstrating the usefulness of new stuff, methods of testing for and demonstrating complex emergent properties (when it is going to break). All that is systems engineering. And there's a lot more.
More importantly , it doesn't mean that the world doesn't use it! For me the heart of it is complexity. Understanding that ALL things are complex, because even something simple like a spanner is nested within other systems, cultural, legal, environmental. they interact with the spanner, and make its behaviour hard to predict. Those ol' unintended consequences.
The purpose of systems theory and systems engineering is to assert that we know damn well that smoke affects insects. We know insects are everywhere. We know the smoke has been a constant. If we asked A or B we would discover that they do not suffer from insects, and this is unexpected.
Really good engineers have always been systems engineers. But the whole point of the profession of engineering is to codify and formalise what would otherwise be art.