Concentration/number of weapon types in the pre-and immidiate migration period.

[Watchman]

...also it seems to the Anglo-Saxons whom did not adopt it until the 10th and 11th cens.

The Byzantines picked it up from the Avars already in what, 8th century. That it took so long for it to be adopted in western Europe (which was in contact with Byzantine influences along the Mediterranean coast), despite the rising importance of heavy cavalry from Carolingian times onwards, makes for one pretty strong argument against the (already long discredited anyway) "stirrup myth" IMO.