Guild Wars 2

This is whine thread, I know. Feel ashamed for that. I don’t usually whine.
Sorry for bad language and kittens.

Yesterday I was in Orr, “doing” champion undead with random guardian and thief.
Staff, fire-water-arcane, standard event mob kicker build. Not so much single target dps compared to thief and guardian too. Sounds like easy trip, eh?
well
not really
That kitteny kittenish kitten was on me ALL the fight. I was downed like 15-20 times, but thanks to those kind heroes of circumstance, that were ressing me fast enough, I didn’t die that day. Was close enough tho.
Even running away was not an option because that champion was ranged, chop-chopping with his necromancer’ish teeth like a rain of trucks, and all that on my poor 15000 hp. And other undeads around showed some love only for me too.
Easy trip for guardian and thief, yea.

Now how could this happen? Guardian aggroed him first, I actually damaged him for like 1 minute, and then just tried to survive for like 5-6 minutes. I also remember sorrow embrace storymode golem boss which preferred elementalists above anyone else.

So, my question is: how this obscure aggro mechanic works and why am I and any other elementalists out there being forced into toughness-vitality zero damage nonsense every time we aren’t doing events or www? Wasting 3 silver for retrait every time you’d like to www or event sinks money faster than you could say “mr. champion loves squishies”.
I really don’t understand why he keep sticking on mostly harmless me, when he has BIG BADKITTEN NORN and SNEAKY INYAFACE DIRTY FIGHTER right under his nose dealing all damage.