[BeetleB]

You're right, which is why I added more factors in my original comment:

https://news.ycombinator.com/item?id=34902201

I guarantee you that if your application process requires a cover letter, and will not proceed until you upload one, you will probably lose a fraction of applicants.

You can ask them to put the string "xyzzy" in the cover letter as a screening measure. This will almost certainly curtail the bulk of applicants.

The basic idea: Add enough friction to the application process so you'll get higher quality candidates. This is trivial to do.