this game gives lots of medals / levels for advancing (fighting, raiding, collecting debris...), but there is nothing for killing pirates.

Killing pirates is really big part of this game, so maybe there could be medal for it too?

We prefer to encourage the players for activity against other players, not bots.

yes the stronger players already take most of the pirates, without getting a reward for it and making it more appealing 

you try to encourage  activity vs other players then why so huge vesp costs almost no one can fly easy