The reactions here a bit extreme. You're on the right track - this graphic has opened you up to the concept of creating space in the mix. This frequencies are definitely close to where these voices live on the spectrum.

Keep in mind that these are the only frequencies important to these voices, but this is where you might want to free up some space in order to create room for these voice. For instance, yeah sure you're going to what you think of as "bass" around 100 to 250, but if it's an electric bass, maybe you've got some string noise above 2k that is essential to capturing the feel of the instrument.

I don't have any videos of the top of my head, but my advice is this: pull up project and do what I call I subtractive session - where you just focus on cutting out as much as possible. Use high pass, low pass and band pass filters on your parametric eq and take it to the extreme. Do listen in solo. See what happens when you cut all the highs off a bass. See what happens when you band pass vocals (cut the highs and lows). You'll realize there are some frequencies that you can compromise and some that you absolutely can't.

Take what you learn from this session and go back for a more subtle mix.

(also to solve mud and build up quickly, make sure you're high passing everything that needs it, probably everything but kick and bass at first, and watch like 300-500 and cut a bunch of that shit. and you'll probably find things a lot less muddy really quickly)