I would only question if such a thing can be done with a reasonable expenditure of time and resources. Make the pet battle reward “normal” experience for the first battle, then reward no experience for subsequent battles.
And also allow no experience awarded for pet battles that are not on World Quests.
Incidentally, I just now fought Spineleaf (who is on a World Quest awarding 20 charms). I used Unborn Val’kyr and Ikky, plus my first level Mechantula.
Mechantula is now a fourth level pet for doing nothing other being swapped it in and out without attacking.
Addendum: I’m a little surprised at the responses to this change. To be frank, some of you are being ridiculous. When I first started collecting pets in Legion, and in a mad campaign to acquire and level all the pets I could get my hands on, it never even occurred to me to complain about lack of suitable content to level my pets with in Legion. I simply went to Draenor, then went to Pandaria. And I generally levelled three pets per day doing this, from level one to twenty-five.
I thought it was a godsend. I had the means to help me catch up to the more seasoned pet collectors who’ve been doing this for so much longer than me.
I’m just not understanding this vehement demand to have the means to level pets in current content. Traveling to Draenor is done with a simple click of the Hearthstone. Doing the circuit, you will have a pet leveled from one to twenty-five in less than forty minutes. And another click on another Hearthstone will have you right back again.
Is this really such an unendurable hardship for you?
Pandaria is access by clicking on a Hearthstone to Dalaran, then taking a portal to Pandaria. You’ll do every Pet Battle Master in less than an hour and a half. And you’ll have leveled two pets from one to 25, and another one three fights short of twenty-five.
Another click on another Hearthstone will have you right back where you started from.
What is so difficult about this? What is making you stomp your feet and gnash your teeth, snarling, “No! I want to level my pets in BfA!”
It’s like listening to Veruca Salt in “Willy Wonka.”
“I want today! I want tomorrow! I want to wear 'em like braids in my hair and I don’t want to share 'em!”
The Tamers in Pandaria and Draenor give more experience, they pay you and occasionally you’ll get something useful in the reward bag. I think Draenor and Pandaria are absolutely wonderful for leveling pets.