Probably the best way to approach this question is probably to beg the question: what makes you think that you will only get one definition of fascism, even if you limit it to the leaders/thinkers that you specifically mention? Based on my own experience, this does not really hold true. Certainly, there are many, many shared characteristics between each vision of fascism, but they remain distinct visions that emphasise differing, and often conflicting, aspects of fascism.

Giovanni Gentile saw fascism as a way of marrying the religion and state. Being an organic citizen of the state, acting in concert with others who have given themselves completely to the state, is treated as a kind of ultimate religious experience. Going to a fascist rally is supposed to be the same (or better spiritually speaking) as going to church. For Gentile, fascism was the new religion that was to replace "decadent" Christianity. You can see this expressed in works like Fascism as a Total Concept of Life.

Moseley on the other hand saw fascism as a synthesis of Christianity and Nietzschean philosophy with Oswalt Spengler's Caesarism. You can read about this in Christ, Nietzsche, and Caesar. So already, we've got a direct conflict in how fascism is supposed to relate to christian morality, but that's not all. Although Moseley does claim this kind of religious heritage or connection for fascism, he does not have the same mystical interest that Gentile shows--the immediacy of religious ecstasies created in state service just aren't there in Moseley's writing. So while both Gentile and Moseley claim a spiritual element to fascism, they neither agree on its exact nature, nor how that spiritual element should be related to.

Mussolini is no exception and has the added benefit of contradicting himself multiple times in his history of representing fascist ideology. A good example off the top of my head would be his relationship to Catholicism, which changed from hostility to allegiance. Before ascending to power, Mussolini had been an avowed atheist, authoring anti-clerical pamphlets and fiction. Historians like Robert O. Paxton attribute this change to realpolitik--the fascists found an allegiance more beneficial to gaining power/staying in power than being enemies with the catholic church. Of course, this explanation can't really be derived logically from Mussolini's self-definitions of fascism that predate that allegiance.

In the same way that modern day fascists cannot fully agree on a single definition for self-identification, neither could the original crew. In an online forum context, where pretty much everyone present is some kind of fascist or nazi, these differences come into focus and become evidence for establishing hierarchy in the group. On the other hand, the disagreements tend to fade into the background when they present to an outside group that opposes their ideology.