Idk if you remember but just to remind you luffy is an emperor
He has his own crew, fleet, allies, and territories at his disposal. Hancock literally has no reason to team up with any other emperor that would want to offer her protection because she has luffy
Idk if you remember but just to remind you, do you remember when Green Bull was about to take over Wano single handedly?
Do you remember Yamato staying behind to protect the island even though its been her dream for 20 years to sail the oceans?
Do you remember her lying to Momo and the rest, saying she was staying to travel all over Wano in order not to hurt their feelings, on the suggestion/order of Zoro?
Do you remember Luffy saying thank you, Yamato, that sure takes a load of my mind? Knowing fully well even someone as relatively "weak" as Green Bull is enough to take out Wano by himself if Yamato is gone (forced to stand down). Never mind Shanks, Mihawk, BB or a big Marine Fleet arriving.
If say Amazon Lily is attacked again it puts Luffy in a tough spot. He doesn't have the resources to defend all his territories. He also lacks the reputation of Big Mom, Shanks, Kaido or Whitebeard that would kill any intruders (likely same with Blackbeard).
Luffy would probably need to send Zoro or Robin, killers, to send a message. One would get lost and the other is his trumph card. CG on the other can pay random pirates to protect the country together with one Shichibukai as commander, like a Buster Call.