Really even HRE, England, Castille, Aragon, Hungary?
There problem the quote goes to is that there is no
feudalism.
There are
feudalisms.
Each distinct enough that they are not really the same thing yet all of them routinely put in the same box.
You have German feudalism, that branches into specific regional expressions of the concept.
English feudalism, different kinds of Iberian feudalism, etc.
It is like talking about 'democracy'.
France, Germany and the US are all democracies, yet there difference are probably as many as their overlaps. Widen the focus and it becomes even worse.
It is the same with 'Volk' (people) or 'race'.
One word trying to cover so many disparate things that in an academical context where you want to communicate a precise, specialized concept the word is basically worthless without writing two pages to define which part of the word you want to use.
Which would then be "Don't use it, it is imprecise" and further shortened for the mouthbreathers "That does not exist!"