Honestly, I wouldn't go so far as to say that he has no credibility; I can't really point at any one thing he has said and declare in good conscience "That's hogwash! Totally untrue!" I'd say most of his drivel, at least what I have heard and what I have seen discussed here, is essentially true...but, hey, the guy needs views; he can't just say the same thing that everyone else says and expect to garner a following. So he re-words and re-brands and re-labels old ideas and tries to present them as his own original work.
We talk about seeding our aquaria with biofilter material from established tanks all the time; it works, plain and simple. We are also aware that the bacteria...or Archaea, or organic nanobots, or whatever they are...are situated on all surfaces in the aquarium. It therefore follows that simply bringing in stuff from nature that is already seeded with these little miracle workers will kick-start a new tank just as surely as a skanky old spongefilter from an established tank.
Sure, it's a lot messier and more labour-intensive to drag in a bucket of stinky crap from the bottom of a pond, but it probably has a certain quasi-holistic appeal to the Earth-mothers and hippies who feel that Gaea is now bathing in their tanks.

Or, if you have no established tank, it may be the easiest route to follow.
And I'll be honest here; back when I was a kid and had just started to read about the mysterious organic goings-on that my shiny new undergravel filter was setting up in my latest 5-gallon tank...I did this same thing many times. Several sources suggested or encouraged this idea...it wasn't even original back in the 60's and 70's! They even went so far as to suggest sourcing your bucket of organic crap from a woodland pond or other body of water that did not contain fish, claiming that this simple caution would be instrumental in avoiding the introduction of many or most fish pathogens; very logical...but now new.
One thing is certain: the only dirty used sponge filter that I am dropping into a clean new tank is coming from one of my own aquariums. I don't want someone else's filter, stuffed chockful of someone else's problems, squeezing out its mysterious juices in my new tank. I think a handful of leaves from a woodland pond is far preferable; I just don't think that this idea is new or in any way earth-shaking, and I am not trying to make money on the internet by presenting it as such.
I have also used this type of material many times over the years as a first-food source for freshly-hatched fry. Commercial fry foods were not easily available, at least not in my area, for much of my aquariological career. If you had small species of fry, like gouramis and many others, you needed to culture infusoria and/or green water for the first week or so if you wanted them to eat. I was no dummy; I knew the difficulties associated with explaining to my parents why I had multiple jars of "filth" percolating on a windowledge...and I knew that there was a giant infusoria culture ready and waiting for me in the nearby woods. That was an easy choice to make.
Finally...look at his tank, the one behind him in his video. That is the sort of tank that works and results from his approach. Large, heavily planted...and very few fish. Not many aquarists today will be satisfied with that; most people buy their fish by the bucket and add them to their tanks the way a fishermen stocks the live-bait-well in his boat; i.e. pour in a few dozen fish and hope some of them survive long enough to do their job.
So, Fishy Father has, IMHO, literally nothing new to contribute. In fact, I think that, if anything, he is muddying the waters for new aquarists; he tells them that a lot of what they may have read is wrong (even when it isn't) and then presents all this re-worked terminology as though it represents new ideas (when it doesn't) and makes it sound as though his own sheer intellectual horsepower allowed him to be the first to perceive this truth (which it didn't). I am forced to award him a place of honour in my Aquariological Scam Artists Hall of Fame. I'm putting him in right next to Father of Biocenosis Clarification Baskets; I'm not going to name that guy until after I buy some more stock in kitty-litter companies...