Well, I base my opinion on a couple things: (that low tenancy to clog was about lavarock, which gets covered in mulm and is impossible to clean, let alone large chunks have very little exposed surface to allow nitrification bacteria to flourish.)
Water has what, 7-8ppm of O2 at about 80F, our atmosphere has 209,000ppm
So, pot scrubbies do a great job in wet/dry because of their porous nature, and decent surface area (as far as wet/dry media go) aswell as it lets water flow in through it in an acceptable way.
Submersed media has only a fraction of the O2 available, which limits the size of the bacterial colony considerably, so you want media with very high surface area and that can be placed tightly together without compacting and restricting water flow.
As respectable as Pot scrubbies surface area is, it pales in comparison to the surface area of media made to be submersed.
You can achieve a higher surface area per volume (I think, I'd need to double check) with media like Matrix or Eheim's substrat pro vs pot scrubbies, which I feel really makes it more suitable for the smaller space inside canisters.
Adding an airstone under bio media is a great idea. I doubt it makes the submersed media any where near as effective as media in a trickle filter. It definitely will improve the O2 levels if there's enough surface agitation and current from doing it.
I think that makes sense, I'm a little tired.
