4 hours over two steps to get to the human part? I wouldn't mind it. Last company I successfully interviewed, I spent about 2 hours on the phone with different people + a lot of e-mail exchange, before I got to 4 hours long on-site.
That's asking for too much upfront before the candidate can even decide if the job is a good fit. Job descriptions alone don't tell you much. That's where the phone interview comes in. It's a two-way street.
I think when your company comes up with a hiring scheme, they need to analyze it, understand and be cool with the kinds of applicants their system is screening out. In my view, most SV tech companies' practices tend to screen out the "skilled professional who's currently semi-comfortable at her existing job" and filters in the "desperately needs a job and will jump through hoops and put up with whiteboard hazing to get one." Which class of applicant does your company want to court?
[^]: I consider myself "reasonably-competent" and the 100:10 ratio was about what my last job search was like a few years ago.
I understand this was the goal. You can either waste your company's time or the candidates' time. I don't think there's a way to preserve both. Given that your goal is helping your employer, this seems like the sensible thing to do.
If as mentioned previously wasting candidates' time filters out the most competent people, then you're not helping your employer.
Also, I object to thinking that someone's time needs to be "wasted".
Also, from experience, I've never come across a two hour takehome that actually takes two hours. Everyone always says not to spend more than two hours on it, but I can't exactly turn in an incomplete assignment.
I'm glad it is working for you, but it's not something to be proud of. Essentially what you've done is replace the standard 30 minute intro phone interview with a 2 hour SAT.