Fascists didn't claim to be a third way until they were being pumped full of money. Before that they were mostly former soldiers turned into lumpen-proles and gangsters, who thought that they had been sold out by either the socdems, liberals or socialists. It wasn't about perceived weakness or ineffectiveness on the left, it was about how to achieve personal power regardless of rhetoric. One of the reasons leftists are "holier than thou" (which, to be frank, is simply ludicrous for actually existing popular leftist movements of the era) was because of fascists stealing their popular messaging and language with no actual intention of attempting to deliver on those promises, and in many cases, do the opposite of what they were advocating for.

And this is besides the point that, in practice, fascists are liberals without a pretense of liberal philosophy or civility fetish.