Would disagree. If one has a good generic cover letter plus CV and a very good and wanted profile this would work.
Why? Because it's a number game and better send many standard applications than few individual ones. Leas work and better result.
Also, if you advocate for playing the numbers game then you can't complain about recruiters doing the same.
So, maybe his CV is just not good or has some huge mistake and it's not about personalized cover letters?
However, in the high demand market of software engineers an individual application is the not the key of getting a job. Not at all. It's your profile (is is good? does it fit?) AND that you applied at all. Just guess why devs get dozen of headhunter calls per week without writing a single cover letter...
OP is actually above average by having an actual side project. He just needs help with his resume or application.
Good point, I agree