You throw out 900 resumes between step 1 and 2 because they didn't manage to submit one without tens of spelling mistakes?
I agree though that having everyone write a cover letter, that they can write in their own time, and that you can read in your own time is preferable though.
Better yet, just leave off on the cover letter requirement.
When we looked for a Django dev we got two applicants, and the good one of the two only wanted to work freelance. Admittedly we were looking for some experience.
A lot of it is situational. A company in San Francisco hiring a junior Rails dev will probably get a LOT of recent bootcamp grads as applicants. Last I checked, most bootcamps were still focused on teaching Rails. So that's on factor. I was recruiting for Rails in SF, so that's part of it. You learn to optimize for challenges you have.
I agree though that having everyone write a cover letter, that they can write in their own time, and that you can read in your own time is preferable though.
Better yet, just leave off on the cover letter requirement.