the thread i linked to i was told literally "An airpump does not add oxygen to the tank" and that air bubbles coming from a pump do absolutely nothing to help aerate a tank, aside from the surface agitation that they create, and i disagreed.
in my large american cichlid tank, i had plenty of surface agitation from the two filter outlet hoses splashing in from above the surface, but the fish were still gasping at the surface, until i added an air pump and bubble wall, now they are breathing easy. i also note that the air pump is much, much quieter than having my filters create surface agitation, that was quite loud, lots of splashing and whatnot