...and there's an implicit premise in your post that a "complete martial arts system", whatever that is, is what we all want and need.
This is something I really don't get. When you buy a car, do you expect it to be the be-all and end-all car, the car that can do everything? Well, no doubt some people do. We call those people "crazy". Normal people just look for a car that's right for their purpose, whether that is transporting four kids to soccer practice or hauling blocks of cement to a building site or going as fast as you possibly can around a track.
Or, if you want to put it in a martial context, what's the "best" fighter? Gee, I don't know. Put me in one situation and I'll take Mongol light cavalry, put me in another situation and I'll take a seasoned bouncer, and in another I'm definitely going to want a Marine platoon sergeant.
Given that, for the large majority of us, our fighting really is purely theoretical, and any fighting we might possibly encounter is within a specific context, I don't get the endless froth and fury about a "complete martial arts system". Even if such a thing existed, which it doesn't, it's not what any of us needs. If someone finds something sufficient to their needs, why would they look elsewhere?
Best fighter... hmm. I'm going to have to go with the zerglings. Never liked having to strategize too much, just go all ZERG RUSH
. So, okay, maybe playing Starcraft is about the closest many of us will come to an actual fight, or one where martial training is really necessary or expedient.
On the other hand, that means the practice of martial arts should at least be helping us out with everything else in life that we do actually do. So is aikido, which for most is a combined study of techniques of twisting people in funny ways without stopping their momentum with a cool peace and love philosophy to back it up, really offering the most it can, or could it offer more? I very much think it can offer more, and that's because in aikido we spend an awful lot of time worrying too much about we're doing to other people, rather than spending a lot of time on ourselves in isolation. It is not uncommon that I spend several hours a night just working in my own body, whereas I would not have thought to do that before or understood how IS could help me. I just could not really conceive how there were some issues of vital importance that could only really be trained outside the dojo, not in it. That alone is a huge beneficial change it has made to my practice.
From an efficiency stand-point, if you just want the benefits like moving better, exercise, better fitness, etc. just IS training by itself can give you that, in more concentrated form in a much shorter time, than the practice of techniques on other people, but without learning how to fight at all, hell, it'll probably make you a worse fighter by itself just because it'd make you too cocky about your non-existent ability to handle yourself. But without a real world benchmark to test your solely IS growth against, your IS growth will be stunted as well, a glass ceiling set because you never really have a surefire way of realizing just how incompetent you really are. So fighting complements IS exceedingly nicely, they feed eachother.