The bottom row is Channel 2 set for high gain. This setting gives woody sounding leads and lots of note clarity when playing chords. As you can see, it’s not at all how the dials on a Marshall would be set.
As gain goes up, it naturally makes the bass go up as well so you have to dial it down. That’s a Mesa thing. Even though mids are where guitars live, these things have so much that it just congests the frequencies. Right about where I set it is where the mess goes away.
Treble and presence are more what you’d expect so those go wherever your ears tell you to dial them.
Master volumes are mainly for overall volume. I think it depends on the Channel, but generally speaking, you don’t need to turn it up to increase gain. Mesas are all pre-amp gain so you can segregate the Master as strictly a volume control and Gain strictly for adjusting how dirty you want things to be.