You can go look at the old Predictit market if you like - it's still around[1]. You can also check election betting odds[2]. Clinton hovered around 60-80 in the week or two before the election.
Even if it were 90%, I'm not sure that's an indictment of prediction markets. A probability of 90% means that 10% of the time, the other thing happens. It's a bit like saying "wow, it's cold today; I guess global warming isn't real." You'd want to to an analysis across many many prediction markets in order to see if they're generally accurate. That already exists, it's here if you'd like to look at it[3].
We have no way of exploring the multiverse or running the same election more than once, so there isn't any evidence that the payout from a prediction market matches the probability of something happening. It's just collecting the predictions of people who are willing to bet money, weighted by how much they spend, and calling that the prediction. I don't think rich people are necessarily better than not-so-rich people in predicting something not related to their expertise, but prediction markets are weighted according to how much was bet.
Is this a response to the metaculus track record, which is an aggregate of the accurate of all predictions ever made on the platform, and shows that predictions fall close to accurate probabilities? Which part of the track record do you find fault with?
Their FAQ says that they aren't a prediction market, and they operate differently. People aren't placing bets, so it isn't weighted in favor of the wealthy. They weight people based on past prediction success.
#3 makes it look like things predicted as "very likely not" (10-20%) and "very likely so" (80-90%) tend to be biased towards the contrarian view. Does Metaculus have limits that make it unprofitable to make bets things that would push them outside the window? Anecdotally I've seen quotes from prediction marktets that show a surprisingly high chance for things that are incredibly improbable (to the point that I would call them "impossible" in casual conversation).
I've been snagged by a few markets that were in the high 90s or low 10s and looked like free money, but ended up resolving the other way. It's usually either 1) there was some subtlety in how the market was written that causes it to resolve unexpectedly or 2) a true inversion - it just seems like human nature to under-predict how often they actually happen.
In this case the markets are overpredicting inversions; there's at most a very small difference between how often markets predicted at 5% and markets predicted at 20% resolve as "no." Same for the 75%-95% range.