Your present fauna may thrive in that "soup", but you may eventually kill new additions.
After suffering a major "bad" bacteria problem a couple of years ago, causing me to lose several prized Angelfish,
I did a bunch of research on probiotics.
I had simply removed a huge 2 year old Amazon Sword Plant, the disturbed substrate killed 6 fish.
If I hadn't done a Potassium Permanganate dip with the others, I would have lost more.
Not only killed my fish, but a dozen of a friends fish I gave the Swordplant to!
My 125 had zero mulm on the substrate. At a bare minimum, I would vacuum that crap out.
I now dose my tanks with "beneficial bacteria, to reduce mulm, and organic material.
I also feed probiotic flake.
It also populates the "gut" of your livestock, building up their immunity to "nasties"
An added benefit is crystal clear water! ( I also use Purigen).
My 4 year old sump under my 65 had 1 1/2" of mulm, like in your pictures, beneath the bio chamber.
There is now NONE. The bacteria eat it. A lot less filter cleaning too!
Sorry for the long post, just some food for thought...