It is different, one would be grief out of competition, the other is grief out of simple hate. If u cant kill necro it doesnt mean u have to ruin it for others.
But it's still preventing the original clan that started the fight from killing it. Regardless of motive, the intent of taking the kill away is the same.
Personally I wish they'd make it first whack gets lock and aggro could not be stolen from the group that got first hit. Now if the attacking group cannot kill it and they all die, then fine, another clan should be able to come in and kill. But every clan should have their shot at killing bosses without iinterference from other groups.
He didnt ask how is it similar, he asked how is it different, im not from Danu to tell u that although i agree that if at least they cant kill necro, dont grief it, generally i dont like griefing.
Also, IMO, if the rival clan will see the main clan getting necro (which shows their power compared to themselves), maybe it'll be their motive to win on bosses (hopefully fairly) and not by preventing the other clan from growing directly (indirectly would be ur own clan growing, which is fair and recommended, get stronger and compete fairly).