I guess the question is, how does this person "seem really good"? To determine this, they have to have a well written resume that highlights relevant experience. Most resumes seem to be "company xyz - frobulated the frobulation system"
Unless of course your company is interested in frobulation also.
The contrary: "this person has a bunch of experience on their resume that is possibly beneficial, but their cover letter doesn't give any indication they have thought about the role they are applying for. This other applicant shows insight into the requirements of the role via their cover letter, and has highlighted key areas of their experience, giving greater detail about how it will be useful in this role."
Who are you going to pick to interview?
Perhaps this is more important for niche industries, and smaller teams. In a large team you can get good coverage of skills through sheer number of people. In a small team its the alignment of skills is more important.
When hiring (small, niche org) I carefully read all the cover letters.
I understand this hypothetical, my point is: I don't think it's actually relevant. It's not going to be the tipping point.
I should make my contention clearer: I think that companies are extremely unlikely to forego interviewing a candidate that otherwise looks good because they had no cover letter. This doesn't just apply to the best candidates - if any candidate looks hireable in relation to the rest of the applicant pool, they will put them through to the next stage of the process. Once you've actually sat down and spoken to someone, your written introduction is irrelevant.
I do think it probably matters more for small companies, but they're also going to get way less applications to begin with so it's like... You're really going to just not interview good candidates? Really?
"I think that companies are extremely unlikely to forego interviewing a candidate that otherwise looks good because they had no cover letter."
My point is that the cover letter is one of the tools the applicant can use to highlight themselves as a good candidate. It could easily be the tipping point for getting an interview. It can give you some feeling for their communication skills, their understanding of the role / company / product. Though I concede most cover letters are not very well written, mostly generic. In the absence of a good cover letter, their resume alone must stand out.
Of course it could be a tricky situation: choosing between a candidate with a great cover letter and less obviously great resume vs a generic cover letter and more relevant experience listed on their resume.
Personally I would lean towards the better cover letter. They have given a clearer indication enthusiasm and interest in the job. A well written cover letter will explain how their experience is relevant, despite not superficially appearing so. This allows them to show insight into the role.
One point of data: My large organization’s HR department lists a cover letter as a requirement and will forbid us from moving ahead with even a first round interview if the application is incomplete. So yes, really, we can’t interview candidates who demonstrate right at the front door that they can’t/won’t/haven’t read the application requirements.
The contrary: "this person has a bunch of experience on their resume that is possibly beneficial, but their cover letter doesn't give any indication they have thought about the role they are applying for. This other applicant shows insight into the requirements of the role via their cover letter, and has highlighted key areas of their experience, giving greater detail about how it will be useful in this role."
Who are you going to pick to interview?
Perhaps this is more important for niche industries, and smaller teams. In a large team you can get good coverage of skills through sheer number of people. In a small team its the alignment of skills is more important.
When hiring (small, niche org) I carefully read all the cover letters.