Inside an instance they have suspended players for doing it.

Outside of an instance it's fine.

There has been no nerf - it's always been as I'll describe below:

There are 2 rolls involved, Tapper and Killer. As long as the MOB is GREEN or higher to the KILLER the Tapper will get 100% xp for killing the mob. If the mob is not green, then the XP is split based on damage to prevent a level 1 from tapping a level 80 mob and the 80 killing it for them.

At 74 if you can find a ready supply of 80 mobs that give XP you should be able to tap n kill them easily for great XP. Finding the supply outside of an instance is the hard part.