Completing fates in the normal and intended manner still nets very fast experience points gains. It's many times faster than 1.0 experience points parties were. There is no reason to farm Dark Designs like this. Exploiting Dark Designs can grant between 100 and 150 thousand experience points within a 15 minute timeframe. It is effectively ruining the game. Not so much by allowing some players (the ones who farm parties, monopolize the mobs as they spawn, and rabidly, hatefully shout down anyone who tries to complete the FATE normally) to level much faster than others, which it does, but by creating contention and drama amongst the playerbase.