Bache, not sure what you are trying to achieve with this post. As A manufacturer, I would normally assume that you would try to achieve a broadband reasonably flat curve doing little harm as possible to phasing... Not the case? I also look at keeping impedance swings flat as possible. In crossovers, I do prefer to keep part counts down, but if a 3rd or 4th order is needed for driver protection or to preserve phasing, then yes, I would use higher orders. I can only guess that the 10th order slopes that you quote are trying to achieve a brick wall effect to have an absolute start & stop frequency. I hope that you would know those benefits. I've tried very steep slopes and always preferred standard 6 to 24 DB slopes. However, well done brick slopes in active crossovers can be great.
Single way or multiway
The founder and builder of the highly respected high-end speaker company Gauder Akustik, Dr. Gauder, says that using a full-range driver is very bad. He uses 3- to 4-way speakers with extremely complex 10th-order crossovers consisting of 58–60 components.
In contrast, some other well-known and equally respected speaker companies — such as Voxativ, Zu, Cube Audio, and Totem — use crossoverless designs.
Who is right, and who is wrong?