Not if that amazing shot lands at an angle matching the slope. That's the point of baskets on slopes. You have to make a shot that lands the disc on plane with the slope. Otherwise, it's not an amazing shot at all.
I guess we just disagree on the risk/reward of just leaving it on the hill and the risk/reward of changing it in a way that leaves a small more level putting area behind the basket, while creating more danger than already exists below it.
I don't know how he plans to landscape the area afterwards but if the grass is anything but nonexistent you'd have to put the disc on a serious angle from just 120' for it to roll back down with just the slope. Secondly just leaving it as a slope creates no risk/reward other than the standard the closer you are the easier it'll be to make a putt. Not a lot of dynamics there that forces players to think about the shot.
If you change it to what I'm proposing you have a lot of new elements to think about. If you're short and off left or right, hit the side of a mound which now has more slope than the hill you're increasing the likelihood of a rollaway. Even if you land on the small small tops of the mound and stick you still have a putt that's more uphill than it was before because the basket is raised off the plane of the hill with the artificial landing area.
If you're basket high but left or right of the landing area you're still putting up because the basket is raised and because the basket is near the edge of that raised area a miss might leave you still off the landing area looking at the same putt again. If you nail the basket and ricochet towards a mound you might roll down really far.
If you go over the basket past the landing area now you have a serious death putt because missing the basket will definitely put you off the landing area, landing on a mound, possibly on the side of the mound and rolling. At the very least you're second putt is from one of the lower tiers back up.
With all of that I think rewarding people by landing in a 20' circle behind the basket that's semi-level isn't going to easy on people. Not to mention that landing there still leaves you with death putt where there is still a risk of going back down the hill substantially if you miss.
I'm just saying that my way creates a hell of a lot more risk/reward and I'd like to hear your opinion on how leaving it as is creates more. Even if you don't put in mounds and just make the small level area with the basket on the front of it you create more risk/reward. The basket is raised so any missed putts from any direction will be much harder than they were if you just left it as is.