It's not like Coby, a captain, is in command of a whole fleet to take down a hostile nation and a Shichibukai.
It's like in the Buster Call, in which the battleships were filled up with captains, and under the command of five vice-admirals.
Just because we only saw Coby I don't think there's any chance of he being able to take any decisions that wouldn't be viewed as treason at best.
And that if he actually finds out about Hancock's link to Luffy.
In one of latest interviews if I am not mistaken Oda said that when we will see Boa again she will be in danger/ in very difficult situation.
https://digistatement.com/one-piece-jump-festa-2020-eiichiro-oda-message-to-his-fans/
So most likely Vegapunk new weapons proven extremely effective. We also got Marco going to Onigashima- he would be at peace with leaving Whitebeards island only if it would be safe. So either if someone strong enough would be protecting it(like Jozu) or if Marines would capture Weevil.