I sent out screens to ~15-25% of resumes (a higher rate for new grads, lower for seniors, not wanting to unnecessarily rule them out just because they didn't have positive evidence of potential success and didn't know how to write a resume, only ruling them out of there was positive evidence they'd be unsuccessful). That amounted to ~100 per position filled. Around half of those completed the take-home. Some of the rest should have self-selected out and didn't, which is something I'd like to improve if I run a take-home again.
You're right the time commitment wasn't equal. Early on I spent much more time than the candidates designing and analyzing the test. Afterward, their 20 minutes would usually take me <5min (often <1min for obvious failures and obvious passes, the average brought up due to time analyzing edge cases).
I did read every submission though. It wasn't wasted time for candidates.
I've worked at places that would send out 100. People would spend their weekends working on it and we often wouldn't even look at the submissions.