Guild Wars 2

Is it considered a bug/exploit to do the first boss from behind the stone bridge where nothing can hit you?
Is it considered a bug/exploit to pull the ‘combo knockback’ out of groups, until they reset, kill this insanity of a mob, then go back and kill the rest of the group?
Same for the previous to last boss (which has 1-3 combo knockback adds)?
Is it considered a bug/exploit to do the last boss from the ‘up path’ (the fight that spawn plants) from the entrance of the room where all you need to do is dodge the eventual things that spawn from the ground?
I’m wondering because we discovered these tricks after doing TA with a pug (last time we did, it was the ‘hard’ way). They feel as bugs to me because they make the fights absurdly easy (the first and last boss can’t even be called easy, it’s just auto attack and come back 5m later) and I don’t want to find myself banned because I did TA this way.

ANet fails at designing dungeons, simple as that.

last boss can still occasionally kill you even if you stand at the door

1) First boss can hit you behind that rock. And if it doesn’t, plants grow there too.
2) No, you just used strategy.
3) No idea. Didn’t fight last boss from there specifically. But even in places I thought were safe, I still got hit. Just not as often.