Nah the nr1 guy just solo aoe farmed and used shard hopping to always have a big supply of mobs to aoe. Most of the first ppl were mages.
But most guilds did indeed exploit ing dungeons not getting any penalty exp from being 10 or even more ppl. They still got half exp or less compared to a 5man group but that was a tradeoff easily worth it as they could pull twice or more as big and with twice or more the aoe dmg hitting all mobs anyway.
So basicly quad returns for half exp = double xp/hour.