Hypothetically, "agile" is about _allowing_ decisions to be changed at the drop of a hat, without causing pain for implementers. The whole point is accomodating that, that's what "agile" _means_, right? (One can argue this whole goal is impossible, but I don't think it is. If it is, it's a problem for any agile process, not just "low-end scrum." But I think there are _way bigger_ problems with thinking you can plan out all work and schedules a year in advance and stick to it and wind up with anything succesful).

Now, every decision (new or changed) has a cost to be implemented. Some more than others. If you have decision-makers who refuse to recognize that, and think the amount of work they can ask a given staff with a given level of skill to accomplish in a set time period is unbounded -- no process is gonna save you from misery.