Welllll there are a couple of other things that effect swish.

Yes, the weight of the fabric does have an effect, and in general the heavier the fabric the better the swish but the "drape" of the fabric is more important.
Even a very light ladies skirt will swish if the fabric has good drape. One of the reasons I build more fabric into my Contemporary Kilts is that the Poly/Cotton I use has less drape than Tartan Wool. So I have to compensate.
To gauge between two fabrics which has better drape you can take a yarn from each and hold them horizontal. The one that sags more has more drape.

Depth of pleat has a big influence on swish yes, but don't use my figures as an example or ideal. They are only good for my Poly/Cottons. Other fabrics will have different drape so will require a different depth of pleat.
You may not have control over your pleat depth because when using Tartan fabric the depth is determined by the Tartans Sett.

Yes, Military Box Pleats have incredible swish. But it's not all do to the type of pleating in a kilt. Drape, Weight, and Pleat depth have more to do with it.
It just so happens that, in general Military Box Pleats have exactly the same amount of fabric as a comparable knife pleated kilt. What gives them better swish if the way the pleats catch the air when they move. MBP have edges that go in both directions so catch air on both the left and right step where regular knife pleats swish more on the right than the left.

Whether elastic inside the pleats helps improve swish depends on where the elastic is placed and how much room you give it. The elastic was originally put there to keep the pleats down in the wind and when running. It was a modesty thing. Now it's done to keep all those pleats controlled and moving as a unit instead of haphazardly. Any time you keep everything moving as a single unit the look will be improved.

And yes, box pleats swish less than knife pleats in general. But they have a totally different type of swish. Again there are two edges that can catch air from either direction. The best analogy I can think of is Box Pleat swish like willow leaves in a light breeze where knife pleats move more like waves on the ocean. Both pretty, but different.

The one thing you forgot to add was the wearer. I'm in the business so watching pleat swish is like market research to me. (At least that's what I tell my wife because I love to see a woman in a kilt walk.) The swish of a woman's kilt will outdo that of a mans' any day. Go search for the pics of Barb's daughter and son-in-law walking together. Her kilt is moving twice as much as his.

So my list of swish factors would look like this.

1) The drape of the fabric.
2) The weight of the fabric.
3) The total amount of fabric in the kilt.
4) The depth of the pleats.
5) The pleating style.
6) The swagger of the wearer.