For every 1 LLM applicant that this idea would deter, you would also deter 50 humans who simply don't feel like having to send a letter to apply to a job.
At least for me, I'd still rather mail a letter versus input all my personal details and job experience into yet another CRM with a crappy data entry interface.
"Thank you for uploading the PDF with all the information we need. Now, fill all that information in on this page that asks for 2 bits of information at a time and takes a minute to go to the next page. You are on page 1 of 50".