As a self-described student of life (why am I always wearing the dunce cap?
), I think it's important to remember that everyone has "shortcomings." Buyer beware; always.
That is to say: I think a good student can learn something from anyone; and for adults, the ownus of learning is always on the learner. The question is whether that something they're learning matches up with what they're ultimately looking for. I started training in Aikido more because of the meditational side than the martial side so I can see why many other people might have started in a similar way.
I guess I just see how readily folks look to physical effectiveness as the litmus test for what determines an instructor's qualifications and think it important to add that a good teacher is far far more than a mere distributor of content.
In fact one of the things that kept me with Aikido earlier on was the idea that my fellow students were teachers too...the idea being we each have unique sets of knowledge and only through diverse interaction can we glean diverse sets of knowledge.