I think both methods have their place and are valuable. And, arguably, mostly apply to different situations.
Clear writing with evidence is very useful for understanding how things are, or for making a case for how they should be.
Predictions backed by bets are much more useful for understanding how things will be.
The goal of the board is to fight ignorance, not to promote rhetoric. Bets are a tool that can be used to fight ignorance.
The fundamental problem of punditry is that people who are good at making arguments or providing explanations are not necessarily any good at predicting the future. A bet is useful here for a couple reasons. One is that actually making a specific wager requires nailing down specific measurable things, which people are often not that willing to do. The other is that it (hopefully) induces people to go back and reexamine why they were wrong when they are proven wrong (I have learned much more from the intellectual bets I lost than the ones I won). And, conversely, some of the least satisfying discussions I’ve had are with people who are rhetorically gifted but a little too fond of winning arguments to argue in good faith.
When discussing possible futures, I’ll choose the poster with a track record of being correct about specific bets in the past over the one who can write circles around him, because the best explained evidence in the world doesn’t make you right.
I think what I’d really like to see is a forum devoted to predictions that embraces stating clear falsifiable predictions with a definite timeline. Not to what is or what should be, but honest attempts to clearly draw a line in the sand about the future, with a culture of returning to past statements and admitting when one was mistaken. We could confine wagers to that forum, and they could be either monetary or just “I was wrong about this bet made in this post and I admit it” honor-based.