It's taken almost two weeks for Paragon to get this far, with Method and Blood Legion hot on their heels, along with Eksorsus and Moonz, the only other 10-man guild in the top ten, although they skipped Dark Animus the first time around.
Paragon have been leading the pack throughout the race, with the 25-man versions of both Dark Animus and Twin Consorts needing either "tuning" or flat out nerfs for the 25-man guilds to get past them. Paragon took down the Twin Consorts on March 17th, three days before either Method or Blood Legion, so it's taken Paragon a full week to get Lei Shen dispatched. Blizzard has said all along that Lei Shen was a very difficult fight, and we're just now seeing the extent of that. It'll be interesting to see if the 25m version of Lei Shen remains unchanged through the upcoming raid reset.
Paragon now move on to Ra-Den, they'll be the first players in the world to see this top-secret boss in action, but we wouldn't expect them to be free and easy with the details until he's down. They've only got 30 tries to get past him, but they're in a good position, given that they've taken out Lei Shen just before a reset. Unless the other guilds can catch up today/tomorrow (raids reset on a Tuesday night in the EU), they'll have a full week with only 30 attempts on Ra-Den to play with.