I did both, and I felt my main job as a judge wasn't really to decide the winner, but to give meaningful critique so that both teams can get better. I tried to be fair and to decide the winner based on reasonable arguments, but if the only thing you provide is a winner and a ranking, you're not really helping the students much.
I understand the cynicism of the OP as in the upper divisions it can turn into this bizarre free-for-all speed reading contest, but there are alot of students who didn't go all-in, never even tried competing at that level, and still got something valuable out of it.
IMO, the reason why the activity is valuable is because it forces the students to think critically in a way that they don't get to do in other activities. The best students take the time to find new research, to look at what they find and figure out what articles are worthwhile and which are just smokescreens (or "fake news"). But even the less experienced students still benefit because they are forced to argue both sides, which makes them think about why the arguments in one side may be weaker than the other.
Also, well-run tournaments try to match teams of equal experience as much as possible. They have "speed reading" divisions but they also have novice divisions as well. After the first 2-3 rounds they also try and and match teams with similar win/loss records so that even two poorly matched teams have a chance to find their level.
For the most part, even students who only go for a semester or two of debate and never come back are better off than those who weren't exposed to the activity. It may not help in terms of making Democracy better, but it does help students learn to do research, think on their feet, and feel more comfortable about speaking publicly.