Got mine as a random drop from Nyzul static
well before I even thought of leveling PLD.
Just seconding this. There's enough people that want a runic key that you can build yourself a solid static even among casual friends. The biggest problem casual "statics" suffer is when someone misses... You either farm what you can, move on and hope they catch up, or move on then help them climb again. Most of the groups I saw did the first. If you're actually climbing, most of the weapons will drop. Took me 3 statics and the final climb from 35-100 before I finally saw mine drop (two others both stopped at 30...).
You may as well try to get to floor 100 on your own disc but note that most groups are not keen on bringing a PLD to Nyzul unless he's very good at dealing damage. Most stuff in Nyzul is weak; tanks are not really called for.
Best place for a PLD in Nyzul is boss floors. If you're trying to TANK and not DD, you're wasting the spot you're taking up. I went BLU on my climbs - I didn't take PLD in at all. I could have, but BLU offers so much more than PLD. Last resort, though, when you get 100 - you go in PLD for a run and take everyone up to 96. You're gauranteed to get it then.
If I had started the quest appropriately, I would have had atonement a month before I actually got it. I stopped syncing as often because play time came down, so it wasn't until we hit 100 that I got it.
But, I've staved off unlocking Expacion for my BLU until I could do a simple 250 WS's. Some WS's are worth getting ASAP, others are not. For me, Atonement was one, Expacion isn't.