As mentioned, I always bring one with me, never ever used it to the FoH (always offering it), they go from the amp's DI. Why? If You ask me, cause it's exaclty the tone I set and monitor with my amp, always adjusting it to the room and the band mix, just like if it was mic'd. Not to mention You can use the amp's OD...
Watch:
At 14:10-ish they switch from mic to XLR. It is VERY similar, almost identical. And that is exactly the point IMHO.
Good job finding the flat EQ on the amp I guess! Your ears do not deceive You!
https://www.talkbass.com/wiki/fender-rumble-500-frequencies/#3-rumble-500-actual-flat-frequencies
(note that there is the speaker after this as the last filter, so this is still not completely flat coming from the speakers)
My 2cents is if sb struggles with "mud" or basically any "tone", they just dunno how to EQ or what frequencies to cut/boost. Or having a smaller amp then needed, so it farts out/distort/compress/whatever. Mud is not coming from the amp (see video above) but the room. People should identify what freqs are causing it (lows oviously

) and use the damn EQ/hi-pass to make it work.
I'd suggest a multiband EQ pedal to anyone, and just fiddle with the sliders to at least hear what freq. does what.
As somebody wise once said: "a little EQ goes a long way".