Of course they're getting "my" xp, that's the point.
The payoff is that they're paying for it.
I just don't trust anyone to pay me(though I'm sure most of the serious ones would, not the desperate begging type) and I hate "grinding" for someone else.
The game not only enables it, it encourages it because there's a class and sub-class that mainly heals others and buffs them(i.e casts benefficial spells), and for them to actually get any xp etc they have to partner with someone, preferablly someone significantly higher.
So either you get healed and buffed for it, or you get payed, or maybe just because it's your friend, you can power-level them and it's not at all considered a cheat(though I do despise people lazy enough to pay for it, though not healers since that's how their system works).
In memory of Perach, who suffered and died needlessly.
I wish I could have been with you that one last time.