my take on the admissions process is that each candidate needs a narrative. Besides the requisite stats, the candidate’s “raison d’être,” or what makes the candidate compelling or unusual or excellent, must be echoed in the interview, essays and letters of recs. If a letter from some random alum doesn’t support the narrative, if it sounds like a rote favor or somehow gratuitous, I agree it would be useless, or even detrimental. However, if a letter from a noteworthy alum adds more evidence to the candidate’s narrative, it can make a huge difference.