By the late Middle Ages the feudal economy was doomed, faced with an accumulation crisis that stretched for more than a century. We deduce its dimension from some basic estimates indicating that between 1350 and 1500 a major shift occurred in the power-relation between workers and masters. The real wage increased by 100%, prices declined by 33%, rents also declined, the length of the working-day decreased, and a tendency appeared toward local self-sufficiency. Evidence of a chronic disaccumulation trend in this period is also found in the pessimism of the contemporary merchants and landowners, and the measures which the European states adopted to protect markets, suppress competition and force people to work at the conditions imposed. As the entries to the registers of the feudal manors recorded, “the work [was] not worth the breakfast” (Dobb 1963: 54). The feudal economy could not reproduce itself, nor could a capitalist society have “evolved” from it, for self-sufficiency and the new high-wage regime allowed for the “wealth of the people,” but “excluded the possibility of capitalistic wealth” (Marx 1909, Vol I, 789).

It was in response to this crisis that the European ruling class launched the global offensive that in the course of at least three centuries was to change the history of the planet, laying the foundations of a capitalist world-system, in the relentless attempt to appropriate new sources of wealth, expand its economic basis, and bring new workers under its command. … I refer to the social processes that characterized the “feudal” reaction" and the development of capitalist relations with the Marxian concept of “primitive accumulation”… Marx introduced the concept of “primitive accumulation” at the end of Capital Volume I to describe the social and economic restructuring that the European ruling class initiated in response to its accumulation crisis, and to establish (in polemics with Adam Smith) that: (i) capitalism could not have developed without a prior concentration of capital and labor; and that (ii) divorcing the workers from the means of production, not the abstinence of the rich, is the source of capitalist wealth. Primitive accumulation, then, is a useful concept, for it connects the “feudal reaction” with the development of a capitalist economy, and it identifies the historical and logical conditions for the development of the capitalist system, “primitive” (“originary”) indicating a precondition for the existence of capitalist relations, as much as a specific event in time. (p 62- 63, emphasis Federici’s)

I see your point on the transformation part, but I still think the analogy is relevant. In both cases (transformation from feudalism into capitalism and capitalism into fascism) you’re seeing a shift in relations born from the reaction of the ruling class to a crisis. Capitalism was born out of the desire to preserve feudalism that was untenable; so fascism arises when preserving the existing capitalist relations is the desired goal but the outcome is no longer possible.