The same article says "Recent historical research has shown that payment for military service goes back much further than the reign of Edward I, further discrediting the ideas of Stubbs."
I would tend to agree with the "recent historical research" (how recent is recent? This has been known a long time). The fyrd levy, for example, always allowed room for payment in lieu and even Alfred, rather famously, implemented "retainers" paid for more or less on that basis practically as a standing army. Well, more like an army rotating in shifts but still with a standing presence against Danish attempts to expand.
The point is that Stubbs, writing when he did, was of the view that feudalism, even in its "bastard" form, could not extend too far back into Saxon history. I think his stumbling block was that he placed great importance on the notion of "chivalry" and didn't want it extending back into the Saxon era if it could be helped, as this would negate his other favourite hobby-horse - that chivalric behaviour was introduced by the Normans. It was convenient to find a name therefore on which to hang the origin of the concept of "bastard feudalism" and Edward was about as far back as he dared go. Even contemporaries accused him of misstating the case, however his view was one shared by several medievalists of his day.