The way to make debate about truth seeking is to find the right judges who prioritize that.
After the first few times, and after I got a much better grip on my latitude and what was expected of me, I started to make it clear before I judged, "I find it somewhat hard to follow spreading and I have noticed that I tend to consider plausibility when evaluating arguments, please keep those in mind" and usually there is a flurry of quiet re-strategizing before the debate, followed by a somewhat more meaningful exchange. However it has never quite gotten to the level where anything really felt resolved and it indeed always feels like a bizarre "game".
That's a shame. Most tournaments I've been involved with organizing had an optional 15 min training session and/or handed out a one page information sheet. You should suggest something similar if you ever judge again. In particular, such a sheet should begin with something addressing (c) -- "you are in charge, make any decision you want".
> However it has never quite gotten to the level where anything really felt resolved and it indeed always feels like a bizarre "game".
This is mostly to be expected, and is true pretty uniformly throughout the various styles of debate (including those outside the USA). Turns out the majority of high school students aren't very good at designing and presenting arguments. It doesn't help that in the first speeches they are often presenting arguments that they didn't actually write themselves.
The idea of truth-seeking is laughable. You are required to switch sides each time.
Or as to the feeling that nothing feels fully resolved. It seems like that should be expected when the opponents are well-matched; rather than, say, a runaway victory resolved in favor of one side? Even then, I don't think any sports spectator would want a team to actually give up partway through and concede rather than continue.
I'm with you, except for this bit. The side-switching is the primary way for truth-seeking to enter debate. If you only look for arguments for one side, you're a demagogue. Truth-seeking consists of searching for the strongest arguments for both sides. Most people struggle to argue at their best for both sides simultaneously, so debate sequences them.
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.