Party Punch is Pay 2 Win. Bald faced, outrageous, shameless P2W.
When you get something like dozen Favors on a full run of the challenge, getting any of the rewards is going to represent hours of grinding the same challenge over and over.
Or you can buy a potion for 25 TP that gives you a 5% chance on kill to get a favor. That means every ~240 kills is the same as a full run of the challenge. Considering how fast you can rack them up in places like Epic Orchard, that's an insane increase in your Favor earning rate.
I was worried about this before, too. Punch needs to be put on the Favor Vendor itself so you can buy it without spending DP (after grinding a few Challenges at first), or else I dont know how else to describe the item other than blatantly unfair.