There is 0 need to call my idea naive. Feel free to disagree, state why etc.

I don't think rewards are an issue, the issue is as Saccharin said, it's an open world mass event. However, the original design was intended for small 1-2 parties to take on and not for zerg fests. This could help with a zerg fest.

If you increase the spawn rate and number of hunts, then it won't be a large issue that solo groups will be taking care of hunts.

That said, I've seen scaling HP In other games and it did not improve the mass event environment, things were still a zerg fest. I think the only way to get around a zerg fest is to provide incentive to not allow zergs.