Fascism's failure is the same failure as all other forms of authoritarian government.
It requires you to find the right guy to lead it. And then figure out how to get another right guy to replace him when he's gone.
The other end of the spectrum is to give power to nobody. Because no one who seeks power can be trusted.
But that kind of system is anathema to people who want to rule over other people, so it always gets pulled down and replaced.
And then you get the same problems. Bad people with too much power.
I have to wonder if some of the ancient pagan concepts on ruling wouldn't be an improvement.
Elect a king for a year. Give him absolute power. And at the end of the year, kill him.
At least we wouldn't have 80 year old dementia patients running everything.