IMO a senior instructor absolutely should be prepared to consider and advise the student regarding, to use your words (bolded above) how to adjust the techniques to personal anatomical issues ....at least outside of class or in a private lesson.
Equally, the student should not only be encouraged, but be required to inform the instructor of any physical anomalies or conditions that might create problems for them during normal training. I have seen several instances where an instructor's refusal to tolerate any deviation from the traditional norms in training has led to student injuries.
On one hand, the instructor, coach, sensei, or sifu can't be expected to be an expert on physiology and solve every student's physical issues, especially in a large class. On the other hand some instructors act as though they are such experts and push students into doing movements which, for that particular student, are either physically impossible, or worse, possible but physically harmful.
In a way I agree that you describe the ultimate instructors, however as a beginner, not having any previous experience with "MA experts", I mainly have experience with "experts in academia", and if there is something I have learn in life in general, is to not have too high expectations on others. So I accept my problems as mine to solve.
Also the complication is this: The official superficial telling is that, if you can't do this technique, then try to do it as close as possible, as good as you can, and let that be good enough. This is what I have heard in class.
BUT there is a serious problem with this that brings us to the constructing principles and foundations of the MA arts and it¨s techniques. The contextuality, where the optimal way to perform something depends on not just the context, but also the practitioner.
Lets say that constructing principles describe the best way A1=f(C1), to perform something (a block or attack or something else), given the practitioners abilities and anatomy C1.
And the optimal way A2=f(C2) to perform the task, given C2, is not necessarily "as close as A1 as possible, in a linear faishon, if C1 is different than C2. Then to encourage the student associated to C2 to still have A1=f(A1) as its "goal" could be plain wrong, and disrespect the constructing principles.
Instead PROPERLY applying, the constructing principles (and RECONSTRUCTING the optimal moves) based on C2, one is taking the "ideal picture" A1 from the style normatives.
If I put onto my seniors of the style to make this reconstruction, might be asking too much. IT would force them to question the style surface and seek the roots - not roots of TRADITION - but roots of principles of body mechanics and fighting strategy. But if we would have masters that did this, I think it would imply a unification of all styles and MA. This is why I think it is not for a beginner like me to expect this from my instructors. I accept this as my personal problem.