The problem, as I see it, is that Aiki as in Internal Skills can be measured fairly objectively, whereas Aiki as spirituality cannot. So I think it's the IS foundation that's lacking rather than the spirituality, since spirituality can and is reinvented within each individual.
If we're to use aiki as spiritual path then we surely need the foundation of internal skills, otherwise the word loses its' significance (we could just as easily say satori). But with a good aiki (IS) foundation, those who want to pursue a spiritual vision with it can do so. What's more, that foundation does not have to be taught by people whose focus particularly spiritual.
My take on the spirituality thing is pragmatic. The perfect aikido waza subdues without injuring, which is spiritual in my book. But, as many knowledgeable people argue, this is only realistic in a fight when you are very dominant. And that's when the aiki comes in.
Spirituality, in-and-of-itself, cannot be measured, to be sure. My point is simply that these skills can indeed be developed from both, though different, directions, and the results can be "objectively measured" in either case, in that sense. My guess is that O Sensei did both, but that's only a guess.
True, most, by far, who try to "take the 'spiritual' path" (or think they are) don't get the skills though, in my observation. Sometimes the result is to the detriment of Aikido.