You're right, it's not limited to PLD. But I don't see people clamoring to get BSTs, PUPs, or SMNs in their linkshells in the overworld either. It applies both inside and out. If anything, Abyssea promotes a greater job diversity by requiring at least 6 unique jobs to full proc any single NM (MNK/WAR, NIN/WAR, WAR, WHM, BLU/NIN, BLM/BRD). Outside, you could just have a BRD/BLM, WHM/SCH, and any two DDs and you'll be set.