I'm not quite sure where your complaint lies in having legendaries being "OP". As far as I know that's the whole point of legendaries. My guild was by no means heroic FL geared when we started DS (most of us were in the new heroic dungeon gear and LFR gear) and were able to clear normal DS. You have to remember that the top guilds are the exception, not the rule when it comes to how Blizzard designs things. Obviously they don't want to make it so everything is one-shot on the first night because then there wouldn't be a race, it'd just be the first people that log in.

All-in-all I'm kinda torn on nerfs, I think how they have it now where it's 5% at a time isn't too bad but I think there needs to be a limit. I think 10%, maybe 15%, would be good so the raid still maintains the difficulty but still helps out the rest of the population.

Please bear in mind that the only reason world first Spine Hc required 7 mages from a guild with a total of 19 dragonwraths is because world firsts require ridiculous strategies to compensate for their lack of gear. They don't get to farm the instance for a few weeks before they give it a go. They are, to all intents and purposes, severely undergeared for the content they are doing and require their sheer skill and these oddities such as class stacking, multiple legendaries and off the wall strategies to complete their kills.