This blog post really struck a chord with me. At the USC college (the SC not CA one) we have two Aikido clubs. A year ago ours, a Seidokan Aikido club was being taught by a 7th dan and his senior students that ranged from 4th dan to 2nd dan. The new club, a Wadokai club, was being taught by an ikkyu. I eventually met him and asked why he started his club. He said he tried ours and it 'was giving him bad habits'. Really? I still find it hard to believe a brown belt would say he could learn nothing from our teacher. Actually, he was saying learning from our teacher who has around 35 years of experience was actually detrimental.
I don't know if he was right or not, but I wouldn't be surprised to meet yet another 7th dan whose habits are detrimental to your martial health.
Ever consider that he may have been correct?
Anyway, the ranking system was brought in by Jigoro Kano (from Japanese chess, no less!), mainly in his efforts to make martial arts easier to teach to large groups of children. I wouldn't put too much weight on it.