I was going to write a long response but this will suffice. I understand your point that the relatively unconscious function can only hold conscious for short period of time, but my problem is that in that short period of time there will be a battle between the main function and the auxiliary. He doesn't state that the auxiliary can hold short periods of time in consciousness, instead he states that whenever the auxiliary starts to take on a conscions differentiation it suppresses the main function. So even if the auxiliary could attain consciousness ffor a short period of time, it would inevitably suppress the main function in that short period of time. Since the auxiliary can only be possible as far as it serves the main function, it can not proceed to cross over the threshold into consciousness or elose it seizes to be an auxilary and starts to suppress the main function, which would cause some psychological issues, even if for a short period of time.What I think you're saying, and I agree with, is that a person can't have their auxiliary function remain conscious for too long, otherwise it starts to threaten the value of the dominant function, and then as Jung says and you aptly point out, a battle ensues. I think that's very true and makes sense.
But I still think one function above the rest besides the dominant function will enter consciousness more often than any other (besides the dominant), and that function is likely to be the auxiliary function. It will never remain for very long, because to do so thwarts the dominant, but still, it will remain more than the other two functions.
Out of that line of reasoning can be derived the argument that the auxiliary function (whenever consciously employed) shares the attitude of the dominant function (by virtue of the attitude of consciousness in general).
This doesn't conflict with the point Jung makes, that the auxiliary is still "relatively unconscious". It most definitely is, again I agree. It can never be conscious to the same degree and for the same length of time as the dominant. I think this is true, and this is also why I say I think there is practical value in the MBTI interpretation, because by just looking at the auxiliary as being unconscious most of the time, this neither conflicts with Jung, nor does it necessarily conflict with how it will show up most of the time in real cases.
But there will be a certain level of precision being lost if we ignore the other side of the coin, namely, just whenever it becomes hard to say how relatively unconscious my auxiliary function is.
Here I am saying that, while on the one hand yes it is relatively unconscious, the question is how relatively? And in that case, you will see some variation between different people of the same type.
The one person is going to have a relatively more pronounced investment of conscious will in their dominant, and subsequently unconscious will in their inferior, which will make the auxiliary - relative to the unconscious - that much less conscious in general. Whereas in the case of someone who invests less consciousness into their dominant function, their inferior will subsequently be less unconscious, and so their auxiliary function will be relatively less unconscious, do you see?
And for the sake of precision, I am arguing that this distinction is an important nuance to observe, because there are going to be cases where the client will exhibit one or the other kind of ego, and the MBTI interpretation does not really leave room to make this kind of observation because it presents a static model of the functions.
It doesnt matter how relatively unconscious it is because no matter how you define it, it will always and forever be an unconscious function, and because of that it must abide by the rules of the unconscions functions. So it may be more conscious than the inferior but that doesn't make it conscious, it makes it less unconscious than the inferior though. The only true conscious function, is the conscious main function, everything else is unconscious but at different degrees.