Well, like most things, it depends…
The problem with the very low end, at least historically, is that it simply wasn’t reproduced (or reproduced extremely weakly) by sound systems. That’s changed with the advent of VLF drivers and cabinets, but something to remember (especially if using genuine vintage gear).
The other thing is that a “muddy” mix often comes down to having multiple instruments playing in the same range. Piano and keyboard players IME are the worst for that, since they tend to practice solo and they love a full sound. I love playing bass with a jazz-trained pianist, since they are more likely to automatically give the bass player room to play in.
Oodles of distortion on guitar is equally bad, since it tends to fill out the audio spectrum. These are things that the recording or live sound engineer should be dealing with that though - there are ways to separate stuff out so that the bass is the bass.
You’re right though - if the stage mix is loud and has everything in it, boosting a bass guitar’s mids is the way to go. Well, that and tying the keyboard/piano player’s left hand behind their back!