"However, I cannot accept that a focused and dedicated person attending classes twice a week would not be able to attain the same skill level as they would if training three or even four times a week. It would simply take them more "years" to put in the same hours to get there."
Look, to do Aikido with some level of "aiki", which I would hope would be someone's goal, from a technical perspective at least, entails re-programming the body and the mind to act differently than it is naturally programmed to do. There is a certain "critical mass" in terms of training time for this to take place. If you don't reach that, the skills do not "sink in ", they don't ever become your default setting. If "years in" was any kind of important factor, there would be a lot of excellent Aikido out there because there are a lot of folks who have been training in the manner you are talking about and have been doing so for decades.
Barring some sort of scientific study that could verify this over time with a large sample, I am stuck with my own observations from 35 years of Aikido. I haven't seen it done. I have seen people training more than we are talking about and not be very good at all. Some of that's effort, some is talent related and some is the quality of the instruction. What I am saying here is, given high level instruction and an average athletic ability, one could be good at this art with three times a week or more. Perhaps, my standard is different. I see many folks, even whole dojos in which folks seem quite content with the world. But they don't have any idea what I am doing or what my teachers are doing. It is the same in outward form only.
Aikido is about altering our fundamental reactions to threat and conflict. It is about learning to relax rather than kick into fight or flight. It is about teaching ones body that relaxing can make it safe rather than tensing up. It is about learning an entirely different way of using the body. Your brain takes a huge amount of practice and assurance that there is something other than pushing and pulling that is effective. It takes a huge amount of proper and intense practice to convince the body / mind that accepting the energy of an attack rather than defending or retreating is the way to be survive.
This is difficult stuff, even if you are training every day. I just don't get why folks think this can be done at all with a time commitment that is less than what most people spend on their commute to work each week. This isn't just about a set of motor skills. I get the impression that some folks think it's about knowing techniques. If that were the case, then sure, you can put ten years in twice a week and know a bunch of techniques. You can't actually do any of them, but you have tones of stuff you can reproduce. The problem is that it's the "aiki" not the techniques that's important in Aikido (once again , my opinion). I mean, it's the name of the art! "Aiki - do". Aikido with no aiki is simply an "Aikido-like substance" with little or no nutrient value.
I told me wife, who is a former national championship fencer and a beginner in Aikido about this thread and she just laughed... Basically she said, "why would anyone think that they could become any good at an art like Aikido putting less time and effort into the training than a bunch of little girls put into their ballet class?" Take any kind of lesson you can think of and the teacher is going to tell you to practice every day. The fact that we need partners and a mat to do most of what we do is unfortunate but a fact. So we can't carry our Aikido "violin" home with us, nor do most of us have that Aikido "piano" in our living room. So we are stuck with an are that requires that we go elsewhere to have our partners and our mat space.
There is actually stuff one can work on at home. It will make your practice better and certainly stronger. The internal power development work is fantastic fro that standpoint. You can add a whole new dimension to your training without adding any more classes at the dojo. But if you aren't already training enough to reach that "critical momentum" in that re-programming of your body / mind, solo internal power work will just make your ineffective technique stronger.
This is why I "care" so much about this... You can see right on the forum that folks have a desire to do good Aikido... they don't want to be told that what they are doing isn't enough, they will ignore all evidence to the contrary, in order to tell themselves that what they can put in will be enough. If the majority of folks in the art are telling themselves this story, pretty soon there is a collective belief that it's true. Eventually, in order to make that view square with reality, the definition of "enough" will be changed. What used to be a mediocre Shodan would now be be an acceptable San Dan. I have seen this with my own eyes. I have seen teachers whose San Dan tests I saw many years ago, now presiding over tests from students that are not even in the ball park with what they had done at the same rank. Not even in the same universe. And no one seemed to recognize this fact. The teacher even seemed rather proud of the student's performance. This is how reality gets distorted to fit the stories we tell ourselves.
We all have our "stories", all of us. I was lucky in that I formed my "story" training with Saotome Sensei. So my "picture" of what a 6th Dan should look like and what he should know was formed very early on. If anything, my view has gotten more difficult to attain, not simpler and easier. I'm ok with my rank but in my own mind I am not even close to where I want to be, merely good enough to not have to apologize. Being aware of ones "stories" and trying to separate what's really true about them and what's just fiction that makes us feel good is a serious part of our training. On this thread, I hope folks have been given a better context in which to view their own stories. That's the point of discussions like this.