Since I’ve dealt a lot with Kant (though I’m not an “expert”), I may have a few insights regarding your question.
First of all, Kant himself says what you attributed to the neo-Kantians (I personally haven’t encountered such a position among any of them, but you may be right).
But with regard to his words, one has to be precise: for Kant there aren’t “two” reasons, but only one and the same reason. The first time it is pure reason (free of sensory input, imagination, etc.) in its theoretical use, and the second time it is pure reason in its practical-moral use.
Indeed, the practical use is prior to the theoretical use for the following reason: pure reason cannot produce theoretical metaphysical knowledge about the thing-in-itself, but it certainly “presumes” to do so. Kant wants to limit that presumption without giving up the aspiration that stands behind it. Therefore, he not only “permits” reason in its practical-moral use to set for itself those same norms (which are not knowledge or theoretical truth), but even obligates a person to make such use of it.
In other words: for moral rather than cognitive reasons, we ought to focus on the practical use of pure reason. Paradoxically, he says that such a more “modest” approach will indeed lead us to a kind of acquaintance with the thing-in-itself and to an ability to escape the teeth of determinism.
Another way to describe this is to say that Kant preaches the sublimation of our most primary intellectual drives, that is, he advocates transforming them into practical activity that does not exceed the bounds of rationality.

When a dog does not attack its owner but does attack someone who comes to harm its owner, is the dog using pure reason or practical moral reason?

Everything Kant says applies only to subjects, especially rational subjects. In his view, dogs do not belong to that group. Therefore, according to his approach, the category of morality is not relevant to animals.

Thanks, Doron.
I still haven’t gotten home since writing the question, so I couldn’t check,
but I think it appears in Hermann Cohen.
I’ll check and write here, God willing.

Hello Rabbi.
I’m still looking through the writings of Hermann Cohen and his colleagues to find what I attributed to them, but it occurred to me that in fact you yourself, in the columns you’ve published lately, have more than once dealt with the importance of democracy and with giving independent value to human rights and freedom (as opposed to what is common among the average religious guys, who feel obligated to prove it from the Talmud and the halakhic decisors, and to burrow into the fluff of Sifra, Sifrei, and Mekhilta).
True, this is not talk about practical reason as prior to pure reason, but it is definitely pragmatic talk about practical thinking as distinct from abstract philosophy, and not necessarily as its conclusion.
Seemingly, from here the road is short to assuming principled priority as well, that is, striving for abstract truth מתוך an ethical approach (since we’ve already reached the conclusion(?) that ethics does exist as distinct from abstract philosophy and not as a result of it).
Hope I’m not talking nonsense…

I really don’t see any connection to the question of practical and pure reason. And as I said, I also don’t understand the meaning of the sentence about priority, or the sentence you formulated here about principled priority.

As for the meaning of the sentence—I’ll explain.
After all, we apparently have in the mind an effect of pure reason and an effect of practical reason.
It could be that there is no connection between them, and one can think about each of them separately.
I can be a philosopher who, through abstract inquiry, reaches the conclusion that there is a God, that He created the world and human beings, and that He demands of man moral conduct and/or the fulfillment of ritual commandments and/or acting according to his practical reason—a kind of religion of reason. In such a case, practical reason would be born of pure reason.
I can also be a person who is mainly interested in practice, but if I think that if there is a Creator of the world then I have a moral obligation to fulfill His commandments, or alternatively if I think that if there is a God and He gives reward and punishment then it is very worthwhile for me to be faithful to His commandments, then practical reason requires me to invest abstract philosophical effort in asking myself whether there is a God. (And not only that, but any abstract issue that may have practical implications is worth clarifying.)

Seemingly it is obvious that among different people different possibilities among these could exist; the question is whether one has ontological priority over the other.

That is, whether there is necessary principled ontological priority.

I can’t manage to understand the question, and I don’t see the slightest difference between the two options you described. Define practical and pure reason, and give a concrete example, and formulate the question in relation to it.

In your opinion,
does moral consciousness (and any practical thinking) stem from abstract philosophy / in principle need to stem from abstract philosophy?
Or alternatively,
does abstract philosophy stem from moral consciousness (/any practical thinking) / in principle need to stem from moral consciousness?

I don’t understand the question. Can you make it more concrete? An example?

The simplest example possible—in the religious context, that is, fulfillment of commandments as a consequence of a philosophical view (there is a God, and He wants / demands that I keep the commandments), or approaching the study of philosophy as fulfillment of a commandment.

But that really misses the point of the question, because what I wanted to ask was whether, categorically, abstract thinking that proceeds from a practical / ethical approach is flawed, or possible, or even preferable.

Corrected:
The simplest example possible—in the religious context, that is, fulfillment of commandments as a consequence of a philosophical view (there is a God, and He wants / demands that I keep the commandments) as opposed to studying philosophy as fulfillment of a commandment. Is one preferable to the other.

But that really misses the point of the question, because what I wanted to ask was whether, categorically, abstract thinking that proceeds from a practical / ethical approach is flawed, or possible, or even preferable.

I’m done. Unless you manage to come down from the level of general and vague declaration and bring an example and formulate the question in relation to it.

Is the example from the religious context problematic?

It doesn’t seem to me like an example of anything. It’s a question in itself, and even it isn’t clear: is there value in studying philosophy? Or alternatively, should fulfillment of the commandments be done on philosophical grounds? What does that have to do with practical or pure reason? And why are your two options alternatives that exclude one another? Is it not possible that there is value in studying philosophy, and together with that, fulfillment of commandments on philosophical grounds or because God wants it? I don’t even understand the words that I myself am writing here.
Especially since you yourself said that this example does not express your point. I truly don’t know what to do with these questions, unless you put a concrete and clear question here, one that really hits the point, with two options each of which is well-defined.
I think, with all due respect, that the fact that you keep failing to present such an example suggests that even for you the question is not well-defined.