You can compare them yourself (Destiny)

by Korny , Dalton, Ga. US. Earth, Sol System, Friday, September 11, 2015, 13:48 (3458 days ago) @ JDQuackers

The Jade Rabbit [Bungie Armory] [DestinyDB]
Fate of All Fools [Bungie Armory] [DestinyDB]

Their stats are basically the same, but the Jade Rabbit has higher impact and smaller mag size. And of course them both having the "Fate of All Fools" perk is pretty suspicious.

They have the same Mag size (7), but it bumps up to 13 with Extended mag:

I don't know if I would say that JR is "now" FoAF, I just think they wanted a similar exotic but weren't exactly happy with the original version of it. And instead of taking away or modifying the one they gave out to tRiFecTa01, they created a new exotic that was more balanced.

Also, FoAF does solar damage... Who knows? It would be awful strange to have two nearly identical exotics (although the year 2 exotics are basically variants of the Year 1 versions).
Wish we could get an explanation from Bungie on what happened, since FoAF is functional within the game world (the perk bugs aside).