That's probably true, but this: "this adventure is made for 45 DPR 20 AC 90 hp heroes" is much more directly useful than a metaphorical "turn the dial to 11" no? Some old 2e mods, in addition to saying what level they were for, on the cover, would include, on the inside, additional DM information for the type of group they would be most successful at it (I'm thinking the type of advice found in City of Skulls for the DM, for example).Do the default assumptions work for most groups? Probably not. So turn it up to 11. Or 12, or 20. Increase your XP budget to whatever number you need. Try different tactics or limit the number of rests between encounters. The solution is going to vary by group and there's no one answer.
I mean, why not include that? That would be really helpful.