This is not quite a direct answer, but has a bearing on this and similar issues:
If the grad student is able to learn from their advisor so that they can write a better proposal, isn't that a good thing? Or, facetiously, is it required that somehow advisors should not impart useful, insightful, expert information to their advisees?
(Amazingly-to-me, some of my colleagues have said so to me, indeed, that it is unethical to give one's PhD students any help on their thesis work, for example. It was not possible to have a sane further conversation about what "advisor" meant, under such hypotheses...)
Also potentially confusing: there is much mythology promoted on the internet that gives the idea that 20-somethings (perhaps especially in STEM fields?) are "all grown up", and will very shortly become world experts in whatever they're doing. This is horribly invidious, in many ways. E.g., as a corollary, surely one's advisor cannot really help much (not that decades of experience might help: the main miscalculation entailed by inexperience seems to be the failure to appreciate the advantages of experience...) ... and then as a logical distortion of that, one's advisor _ought_not_ help. (Since they can't, anyway?)
In my observation, many talented, smart people waste far too much of their energy by attempting (often for egotistical reasons) to be prematurely intellectually/mathematically "independent" of "old people" (=faculty). In my own direct experience, going to a very good graduate program in math helped me overcome the notion that mathematics was "a good vehicle for ego", even for the very best mathematicians. That is, learning from (and respecting) other peoples' efforts is perhaps the premier skill one should desire.
E.g., if one can pay attention to experienced experts well enough to write a fellowship-getting proposal, one is succeeding, not only money-wise, but in terms of assimilating the larger mathematical culture and expertise. It is absurd to object to this. It would be more to-the-point to consider the relative failure of advisors who decide... for whatever reason... to with-hold such guidance. (Teachers who don't teach? Advisors who don't advise? Etc.)
Still, yes, I know, there are popular beliefs that are at extreme opposites of the above.