My first ever hatch I felt that I needed to assist as I noticed many of the situations you described above. I had great success and all ducklings grew up to be very healthy and strong. My next hatch, I decided to not assist and although all 3 ducklings hatched, 1 died within 4 days and the other within 2 weeks and I believe this was due to stressful and problematic hatch.
Sometimes, I think that you just have to go with your gut feeling, despite all the comments and advice telling you never to assist.
Thanks for an interesting read.
As a caution, Assisting should not happen regularly. If it is, then work on incubation issues.
I love the video at the end of this excellent article! Very good explanations of how and when to make decisions, supported with many pictures. I feel more confident to help my future ducklings hatch, once i decide to incubate my duck's eggs.