What do you consider griefing? Because short of having a massive unfair advantage over a host typically the point is to make a host struggle as an invader.
This is the problem. PVE is already designed to make the host struggle. Any added complications IS an unfair advantage over the host.
But you do realize in a duel if you're consistently beating someone that's essentially ruining their fun right? No one has fun getting their booty soundly handed to them often. I guess it would be better to say you prefer fighting people who want to fight.
Losing is a part of competition. Only immature people have their fun ruined by losing a duel. It's a difference in what you signed up for.
The duelist signed up for a duel. They know they can win or lose. If they get mad that they lost, then it's their problem.
The invaded didn't sign up for an invasion, unless they are specifically running a gank squad. Some people just want to coop or need the help with the area.
And if you say, "You signed up for an invasion when you used an Ember", then I am going to counter with, "You signed up to get ganked when you decided to invade", because it is exactly the same thing. Just because you invade, doesn't mean you want to get ganked, and just because you play online with Embers doesn't mean you want to get invaded.
Again, I'll reiterate. As an invader, you ARE NOT looking for a fair fight, and you SHOULD NOT expect one in return, let alone an advantage against the host. If you want a fair fight, then go play in the arena. Otherwise, quit complaining. From Soft has had 5 games to modify this. If they wanted you to be able to murder the host easily, they would have kept the old invasion styles in Demon's Souls and DS1.