Marine HQ aren't dumb to send all their Admirals
It is said that when a Shichibukai Title is Revoked, they would send an Admiral
But it doesn't mean that when multiple Titles are Revoked, then they must send all of their Admirals, that is Dumb
Fujitora is the One clearly tasked to capture Shichibukai, & it seems he started with Hancock
So the Protocol is simple, once Fujitora captures Hancock, he will rest & then Target the Next Shichibukai & so on
No one said that they must be Captured Day 1, but the point is that an Admiral will keep chasing them