ABB, packing a suit in a duffel is possible but tricky. Packing a suit in a soft bag that is shaped like an Airboss is rather easy. I do admit though that it also depends on how big your suit jackets and trousers are.
Here are some tips for packing it in a duffle that apply similarly to more suitcase like bags.
The first thing that goes in the bag are the pants. Fold them together at the leg crease, all seams neatly aligned. If they have no pleats (straight front), the waist goes in the suitcase first lengthwise. Let legs hang out. If they have pleats the legs go in the suitcase first, let the waist hang out over the edge.
Then fill your suitcase with everything else except the jacket. Now fold the pants over. You have just avoided the knee bent and steadied your pants so they cant move and wrinkle.
Now use the jacket folding technique from the video. If the shoulders aren't very large it should fit on top of the trousers in the duffle's main compartment. The Airboss for example is wider than a duffle. That's why it will be easier there.
Another simple option if the jacket simply won't fit in the duffle is to carry it between the handles. Just use the video technique again and place it between the handles. I also think that looks really dashing and debonaire.
Till