Although Athene's method in instances was indeed nerfed, it still works to some extent in outside play. I was levelling a 5th shammy to join my 4 already at 70, and found that it was more efficient to group with 1 shammy from 35+ and quest around with him blasting through stuff. At around 55 I started experimenting with tagging the mob with the lowbie and killing it with the highbie, I found that in general this actually generated more XP per mob than solo killing.

Now I'm not quite sure what level it was at, but I think when I hit 63 on the 5th shammy, I could remain out of group, tag it with the 63 and still get FULL XP. Having noticed this, I added my other 3 shammies to the mix, and saw that yep, full xp for the 63 as long as he tagged the mob 1st. It'll be some formula related to the mob level and the player level and the other DPSers level similar to the way Athene's Method used to work, but I can confirm it still works solo.

As an example I ground out half of my last level (69) with backup from the 4 70 shammies mainly on the L68 elite demons in the camp forges in Nagrand, each died in under 12 seconds and granted a massive 2256XP each (rested).