Although it is true that Sidekick will work well, it is inaccurate to say that envelopes in this context are useless.
No it's not, because they are - read on.
In fact, there are times when envelopes will be the preferred method due to the fact that you will have much greater control over the interplay between the different tracks.
That is precisely what you
don't get. Even if the technique worked at all, you would only be guessing at what the output might be from the settings - there's no way to check this in real time using a preview.
There are also times when you may want to combine both techniques. However, I will admit that this requires far more work and as such it is often better to stick with Sidekick.
There are
no times when you will want to combine both techniques, and for ducking purposes, Sidekick is the only realistic way to do this, unless you can find another processor to do the same thing. You clearly haven't tried this - there is no way that you can actually do ducking this way, because the compressor law works the wrong way around, and you end up with the effect working back to front, whatever you do. This has been tried many times, by many people, and
all have given up.
Please stop making absurd statements - you clearly have no idea of what you are talking about.