Is there any way for a high-level toon to "powerlevel" low level toons?

[Moorea]

Another way to level in the open world that I've discovered. It really probably will only work best at low levels.

Use a high level healer to run through a very large spawn of mobs, while self healing. The healing they will do will pull threat. Then run your aoe group in, and blow up the pack on the healer. Obviously this is dependent on mob density/spawn size. However, there are definitely places where you could leverage this. Just make sure you don't heal the low levels until after the fight, if you do, the healer goes onto the "tag" list, and nerfs the xp. As long as the healer does no damage, and only self heals, the low levels will get full XP.

I can heal my lowbies without them loosing any xp

[Mercbeast]

I can heal my lowbies without them loosing any xp

Interesting. That was one of the ways they nerfed it I thought, so I just assumed it was like that in classic so I never tried