The way I look at it is that if I invade you, I can't fault you for doing w/e it takes to beat me and i expect you to; I expect you to summon more people, I expect you to heal and though I despise WoG or force if its in your playbook and you catch me with it, bravo.
As the invader its my job to defeat you in spite of all your advantages, I also invade as a Dark Wrath, knowing they're higher level makes it more interesting.
On a side note I was invaded today on my level 35 making my way through DA by a Darkmoon level 95 showed up wielding Grant and nailed me with a BS after I took half his/her health, he was in front of me and then was behind me, it appeared like lag to me but I was the host so idk. he quit out the second time he invaded me knowing I was level 35 and only interested in finishing the area, I thank him for that.. my point on the side note is that I don't feel the darkmooners are the good guys, it seems to me like its an easy covenant to grief while hiding under a guise of righteousness, the person in my example is a rare breed and all the other darkmooners I've ran into have been just another form of griefer.