I remember back in 2012 InTrade had a market for the US Presidential election, the odds were wrong, stayed wrong for months, and actually got more wrong close to the event. You could get hourly liquidity in the tens of thousands almost throughout (I put on $20k in this market, I wasn't touching the sides, it was incredible).
Most of the people who talk a lot about prediction markets haven't worked in markets. Markets aren't magic. They work better with binary outcomes but they cannot be smarter than the people making bets in that market...and they aren't (I have most experience with financial markets, which just don't work well at all, but have quite a bit of experience with binary markets too...they have only become more accurate as our knowledge about the underlying events increased...if you look at binary markets where knowledge is limited in some way, markets are not efficient).