They said it was impossible? Damn!!! It can't be that hard...
As for revenging during world boss, this is something people go crazy over on my server too. So we just don't do it. If someone makes a mistake and does it, OMG, get ready for world chat horror, especially from one or two individuals on my server who I won't name.
Mistakes happen, so long as they don't keep repeating it every day. Or just use 5 gems for the shield I guess.
But if one chooses to revenge during GW or Banish, it is their right to do so since the game allows you to, and there is nothing one can do about it, but to figure out how to go around it. Like for me, I try not to sink anyone so they have no revenge against me But it is hard to never sink anyone... or take their stake in the arena.
If you sink anyone , they can beat you :PPPPPPPPPPPPPP?