Hello, I'm one of those young people mentioned in the post and I'm partially responsible for our current topic.
My take is that the distinction between "fun" and "motivational manipulation" is blurry in a lot of forms of entertainment, and this blurriness is significantly more apparent in incremental games compared to other forms of media. As much as I don't like to admit it, I think that most modern games (especially abstract ones such as The Prestige Tree) mostly consist of "motivational manipulation".
That being said, I still think there is still fun to be had in this genre. My personal belief is that the fun in incremental games comes from the organic (or at least not tightly forced) discovery of the intricacies of the mechanical systems these games present. The problem is that very few games manage to handle this discovery well. I've also found interacting with the communities surrounding these games to be an enjoyable experience.
As to the notice, I think it's an okay idea but I don't have any strong preference on any one condition (there are a lot of factors to take into account). My primary doubt is whether the notice will work well since people may be reluctant to seek help and could easily switch to an equally manipulative entertainment outlet that doesn't contain a similar notice.