To reverse-engineer this somewhat…From what I have experienced as a student, the best classes have had a logical within-class progression (e.g. going from footwork all the way up to advanced timing and distance). The top level instructors can push the progression to a very advanced level – AND get their students to at least temporarily perform at that high level. In my opinion, the kicker is that some (but not all) of the advanced aikido technicians have difficulty teaching the complete progression and lose students in the process because they have skipped teaching the more basic/intermediate steps. So, in these cases rank does not equal teaching ability.
As far as I am aware, “certification”, typically does not reflect teaching ability, but rather technical ability. (Even in Systema, yes?) I think a formal teaching credential is great so long as one can provide evidence that those instructors are in fact creating better practitioners. Personally, I really like the Federation of Fly Fishers Casting Instructor Program
as a model. In this multi-level system, you have to take a year-long casting instructor course, demonstrate technical proficiency on advanced casting, AND be able to demonstrate common mistakes that fly casters make (recreating them, and showing several ways to correct). Obviously, the main caveat is that fly fishing is more concerned with functionality (do my flies catch fish). For better or worse, aikido as a whole tends to argue about how to define “functionality”, so a certification program such as the FFF would likely be limited to an organization.