It's not an authoritarian statement, it is a fact.

If the frequencies clash in a mix between sounds that you want to separate then you cannot separate them.

If the sound you want to separate is far away from the sound you want to keep then it's not a problem.

The example you posted although you can remove the high pitched tones of the siren it is no more different than I explained to you previously.

This is an example of yeah it's easily possible.

Give the sound clip you are trying to remove the music from to this guy and see how amazing he still thinks it is.

I've been doing sound most of my life, I know what I am talking about.

When you get a "Clash" of frequencies you cannot separate them unless you have the raw audio elements and remix them.

Even though I got the emperor to say "Luke" better I was still bound by the the beginning of the "Lu" in Jaitas sample with the music that was present. None of the rest had anything to do with anything Jaita did.