4 to 5 years to shodan seems awful short to someone who took 8 years (which is on the short side of average in my group). Our minimum requirements are based on days or hours of training. My sensei even has a elaborate preparation rating system that factors in hours/week and days/month.
Your group takes quite a bit longer than the average I would say. In Japan it is not unusual for the students at a university martial arts club to graduate with a Nidan after four years at the school.
If folks were taking eight years to Shodan, and each rank after that typically takes longer for each promotion, we wouldn't have any Seventh Dans and the number of Sixth Dans would be a faction of what it is. I'm not saying that would be bad... but it indicates to me that the time in grade you are talking about is quite a bit longer than what is the norm.
I am not the one who thinks the term "hobbyist" is somehow demeaning. If it offends you, I won't use it. The fact remains that there are varying degrees of commitment. It isn't about being a "professional" or not. I am one of a very small number of teachers who are "professional". Most of the teachers I know still work regular jobs to support their training. That doesn't mean they are somehow less committed. They put every spare moment of their time, every spare dime they earn, every vacation each year and devote that to Aikido.
In point of fact, balancing ones training with a career and family often takes more commitment than being a single practitioner with no other responsibilities. When I was married to my previous wife we had eight kids between us. I had a very demanding job as a menswear buyer for Eddie Bauer for much of my early training career. I had to fight for every moment I got on the mat. There were years when I couldn't get to Summer Camp because I didn't have the money. So I understand about balancing priorities. In my own case, I had career, family, and Aikido. I realized that I couldn't really do all three well. So I combined the career and the Aikido and stayed home with my kids and trained every night.
What you get with a "professional" is someone who has
to deliver the goods. There is no option. There are lots of folks running dojos which are marginal but they can get away with it because they don't have to live off it. So if the dojo simply pays for their seminars they are happy. I have to "deliver the goods" or I don't eat. If I teach a seminar and it isn't inspiring enough to be invited back again soon, I can't pay my bills. If I sell one video and it fails to generate repeat business from that customer, I can't pay my taxes. There are plenty of mediocre teachers out there running dojos and there are many very fine folks as well. But it's difficult, if not impossible, to make it teaching as a profession if you aren't good at what you do.
As I said before... I am not recommending that anyone put the kind of time and effort into his Aikido that I have... Get a life, have a job that pays, spend time with your family, have money for your kids college, have a body that isn't hosed when you are fifty. No one sensible does what I have. One does it because they are driven to it; because they simply can't see themselves doing something else. So don't think I am being demeaning when I said "hobbyist"... they are the ones that have lives that actually make sense. They are the "normal" ones. But I cannot think of a single great teacher with whom I have trained who would qualify as "normal" in this sense. So the folks who don't wish the art to take over their lives, who just like to train, who don't care about advancement, etc should be darn glad that there were crazed folks who were fanatical about their training or otherwise there would be no top level teachers to train with.