^ well there are great advantages in remaining anonymous though they are powerful they're not the only powerful beings in their world ( in fact one of their strongest got taken out by a relative newcomer), they were against the mafia this time what would they do if others go against them like legitimate governments, or the Hunter society, or the likes of Gin Freeks? Even powerful people will succumb to constant harassment by weaker opponents in the long run.
about Hisoka yeah he seems rather tame,although he is an accessory to the murder of that Auction guy killed by Matchi. Guess his mind is focused on something else,his target.