My diagnosis is that he is overworked. The solution would be to drop half of you and send you to other advisors. I doubt that he is just lazy if he is "well respected" in the field. I doubt that this is an uncommon situation at high level universities with top advisors and active students.
It isn't unethical if he is being diligent even if he is "late" in giving you feedback. There are only so many hours in the day and he is entitled to a life.
I see two possibilities for moving forward.
The first is to seek feedback among yourselves. You have a dozen people who are at least somewhat familiar with your work. You may not be able to get final approval but if you all put less pressure on the prof he may be able to respond in a more timely manner.
The second is to only ask his advice/permission on vital things and then only by extracting the essential in what you need advice/permission on. If you send one page requests rather than 30 page current versions of a paper it is easier on everyone.
One technique I used with students for review of subsequent versions of work was to have them also send the earlier version as well as highlight changes in the latest. It can be very easy to provide feedback. I used paper, so no paging or technology beyond a pen was needed for feedback.
So, work more among yourselves and reduce the load on the prof.
Complaining isn't going to get you anywhere.
I also suggest you look at student outcomes after graduation. Do his students wind up with a career? The market is harsh now, of course, but if his students get placed as well or better than can be otherwise expected, then it might be worth the short term pain.