But I don't believe it's necessary to train every day to become "any good"... of course it's nice if one has the time.
It all depends on what your goals are. Everything you said is true... but who are the models for our training? Is it about what we want to or feel we can put in? Or are our teachers the model? If our teachers, who paved the way for us, represent the model we are striving for (and I am not saying that it is for most, or even many, practitioners) then we need to look at what they did to get to where they are.
Without exception, every senior teacher of Aikido with whom I am familiar spent some significant period of time during which they trained virtually every day, often more than one class each day. Ikeda Sensei told me that, remembering Mary Heiny Sensei when she was at Hombu Dojo, she not only trained every day, she trained in every class every day. Hardly anyone trains in all the classes... they start in the early am and go til the late evening. So, if Mary Heiny Sensei is someone we are striving to model our training after, does anyone think they can become as good as that by training a fraction of the amount she trained? One could make the same argument about virtually any of our teachers.
Everyone wants to feel good about what they are doing. Everyone makes the commitment he or she feels fits into their life as they currently live it. But what must it be like to be a teacher looking out at the student population knowing that very few of them are even trying to be excellent at the art, much less master what that teacher is capable of passing on.
Every year I go to big events at which my own teacher is instructing. This man trained with the Founder and the other post war giants of Aikido for 15 years. I watch as he tries to teach something more advanced and cannot because so many of the people are simply not training hard enough to come back each year better than the year before. So each year he tells them the same things are wrong and they go home and come back the next year with the same things wrong. So he can't teach what he'd like to teach because the majority of the folks aren't ready for it. And they won't be ready for it the way they are training.
So, what happens is that the art begins to adjust to the capacities of the folks doing it. Rather than have a standard that is too high for most people, which would certainly be demoralizing and cause large numbers to quit, the standard changes so that folks can get a win, feel included, pay the rent on the dojo, etc. This changes the whole culture of Aikido. If the standard is now set by the hobbyist, rather than the seriously committed student, then you end up with lots of dojos but none at which one could become excellent. I travel a lot and see lots of dojos around with all sorts of folks. But at very few would I honestly say one could become really excellent at the art.
The fact of the matter is that, if they decided that they really wanted the standard to be excellence, if they were to insist that the dojo be geared towards taking people to a true high level of skills in the art, there would be so few people willing to train that way that the dojo would probably close.
So, we end up with "market forces" determining the character of the art which started as an amazing, complex, and deep practice. It becomes not an art that is hard to comprehend, that is pursued by practitioners who strive each day for mastery but one that the average person understands and can do, with the kind of commitment that average person is willing to make. You end up with the larger dojo paradigm making it impossible for that small number of people who would and could do more to actually do so. You see students who could be great and want to train towards that goal held back by the fact that the majority won't or can't.
I am not really quite sure what the answer is to this quandary. I am fairly sure that most folks, if you asked them, wouldn't wish to believe that what they are spending so much time and effort on is just "Aikido-lite" yet without a critical mass of really serious students striving to match their own teachers, that's what the art becomes.