Fanucci was stupid, Vito was lucky

My take, it was perfect times and opportunity / need -
1. Vito having lost his Grocery store job to tyrant Fanucci's nephew
2. Little Italy - their own Justice League

Vito killing Fanucci, earned Vito his formidable reputation
Quote
Vito to Signor Roberto, Carmela's friend's landlord:
Ask your friends in the neighborhood about me They'll tell you I know how to return a favor

Fanucci's death created a vacuum and Vito stepped in, offering - always with a caveat - friendship and taking care of / settling all Little Italy business, dispensing his 'justice'
and everyone lived happily for a hundred years! as long as they were Vito's friend and no one crossed Vito

It seems to me -
  • “Vito got to be Numero Uno” because during Vito's rise to the top guy, there was little to no competition?
  • No other contenders? to challenge Vito
  • perhaps “NYC Mafia arena” was not quite ruthless, competitive nor Mafia established! when Vito started out
  • then Luca Brasi came along Vito's one man killing machine – Vito was invulnerable

Greed
If Vito's friends would have gone along, wouldn't Vito have been greedy for the “huge money” even if drugs was a dirty business?

Money can be a weapon even more so in their business where every Don is always greedy for money, more money indeed – apart from the money itself, the richer Dons would wield more clout....power, security and able to buy more cops, judges and politician friends

He was slow to anger and to exact vengeance:
Sure thing Vito “didn't pull the triggers in his lifetime” thus leaving a murderous legacy for “I never wanted this for you, son” Michael after - always the nice guy even when detrimental to Michael - Vito's death, to avenge Moe Greene “Sonny and Appolonia, and whacking the other Dons” and condemning Michael to Lifelong misery Thanks! Pop

He was careful
Vito was “careful” until he was careless
after Vito's no to Sollozzo, complacency and slippin' brought him undone and messed up Michael's life

He looked beyond New York:
Sonny's “investment in Moe Greene's hotel” formed “the basis of Michael's move to Nevada and "legitimacy."

You are right “He [Vito] also controlled unions in the movie industry that gave him influence in Hollywood:”
Vito didn't confine himself to just his own backyard and his nefarious power spread it's wings "beyond NYC" including Khartoum's stables