The pyromancy OP stuff also fits Dark Souls in my opinion, not everything is going to be balanced/the same effectiveness. Realistically there will be some things more dangerous and effective than others. That's how life works, I imagine Dark Souls would try reflecting that.

The Early items is honestly something the game was purposely designed for. Considering no attempts were made with patches to cut players off it's safe to assume the developers intended people to be able to do that if they tried hard enough.

Using glitches I can agree is not something the developers or dark souls is intended for. But even if Dark Souls is meant to be a bit fair, it's a brutal fairness. The new player had the same opportunities as others to speed ahead and snag certain items, if one player had the preparedness/initiative to do it and the other didn't that will be reflected in the battle's balance. It should also be noted that the way the game is coded the higher level the player get's the easier it is to fight against invaders cause there's less of a level distance. The invasions were never quite meant to be fair, but meant to more reflect a prey vs predator sort of thing where eventually the prey could turn into the predator.