There is a language problem here.
Gain traditionally simply means additional level - so pulling back the faders reduces gain.
In the context of guitar amps and tube distortion, gain has come (colloquially) to refer to the thickening and distortion achieved by adding levels of preamp gain that overdrive subsequent stages of the amp.
Renegade Prod is, I believe, talking about distorted guitar sounds turning to a muddy mess when multiple high-gain distorted guitar signals (from several mics on the guitar cab) are combined. No amount of turning down the faders is going to reduce the tonal effects of layered distortion.
The answer is that layering thickens the sound and distortion (preamp gain overload) also thickens the sound and too much of either - or a combination of the two - will reliably produce mud. If you're going to layer multiple mic feeds, you'll need to back off on the guitar amp's input gain (or otherwise reduce overdrive distortion) in order to restore coherence while tracking. If you don't do this, you will *not* be able to fix it later.
