I don't think these kinds of "interventions" can do much, because seeing a bunch of people in a room doesn't somehow make you forget what you see in the media,

I don't think these kinds of "interventions" can do much, because seeing a bunch of people in a room doesn't somehow make you forget what you see in the media, or suddenly lose knowledge of what makes you desirable for dating, sex, appearances and etc. I.e. it doesn't matter if you know that certain body types that are currently deemed desirable are rare or unrealistic if you still know that those are what are desired. Also, it isn't just desirability, but our knowledge of associations with health (obesity has undesirable health consequences, regardless if it is accepted or not; being fit over just "average" is again better for health and general ability) that also play into this, and are not changed really by any knowledge of the distribution of body types. At the end of the day, attraction and desirability just aren't purely socially constructed (see: role of symmetry in attraction in basically all species with sexual selection), so you can't fix the problem with naive little things like this.