On some level, this is true. The more likely explanation is that “feminazi” is one of those “democrats are the REAL racists” style claims that were never going to be taken seriously. Insults like SJW have also declined due to an overall stigma associated with them. Even Smug Pepe has declined in popularity in 4chan. Nazism, while still a boogieman, shares more in common with the dissident right than progressivism.
However, the thing about rhetoric like this is that the moderate above is not going to say “What? I was a Nazi all along? Huh, I guess I better listen to feminists, because I don’t wanna be a Nazi!” I simply cannot imagine anyone thinking like this. The more likely response is “Well, I’m clearly not a nazi, but the number of people who seem to leap at calling me a nazi confirms my suspicions that ‘nazi’ really is just a slur that leftists throw at everybody they disagree with.”
This one of the reasons why people get pushed into nazism in the first place. There is no middle ground. The people saying “feminazis” were not nazis to begin with. They were your everyday moderns who disliked authoritarianism. The two sides were fearful, and called each other nazis. The exchange just led some people on the losing side to feel like they did have more in common with hitler than they actually did.