We should have multiple words for mud – like the inuit (allegedly) and snow – to cover stuff from Eastnor Mayhem-style frame-clogging natural concrete through to the watery, gritty gruel that the Dark Peak produces over winter and everything in between.
My experience is that toothy plus tyres are fine for the gruel-type stuff, but less clever on real gloop where they tend to mud-plane rather than bite. I suspect, though I can’t prove it, that there’s some sort of scientific relationship between optimal tyre width, tread depth and pattern and the viscosity and depth of the mud.
Maybe one day someone’ll produce a masters dissertation focussed on just that, but I’m not holding my breath.