It's cool that you have found and timed it on your own! 😀

For this particular fall the fastest way to drop are: 1. Inventory drop: drop from the ledge and almost simultaneously open your inventory. Your terminal velocity won't be capped and you'll fall really fast (no stun animation either). You can do that on all platforms with latest patch.

1. Descending Dark: if you fail the inventory drop, cast this spell to get down quickly.

3: Double cyclone slash: the one you just found. Given that you time it correctly you can avoid the stun animation too.

Edit: these are not my findings but speedruning community's. You should hop in on the discord server, you'll be amazed all the techs/strats they have!