[JayNeely]

"you get the same response rate when you write one-sentence cover letters as you do when you put a lot of effort into them" is faulty thinking. There are many reasons an employer might not be interested in an applicant, and many reasons why they might be. The frustrating part of the hiring process is that not getting a response doesn't provide you with visibility into any of them.

But assuming the cover letter doesn't matter is as much of a mistake as assuming industry experience, or years of experience, or having gone to a particular school doesn't matter.

a) different companies prioritize different things, even if the requirements list is the same.

b) small things can get your application silently rejected (or more often, delegated to a 'maybe we'll come back to them' virtual pile), because employers get dozens of applications (hundreds over multiple positions) and the cost of interviewing is high (and worth noting, much higher than your cost of writing a cover letter).