Is it obviously gambling? Would it be any different if a large financial institution sold prediction market securities?

Somewhere between 70 and 90% of Kalshi event contracts are sports betting. This is obviously gambling.

Much of the remainder is silly stuff like 'how many times will Elon Musk tweet this week' with no predictive value. Again, gambling.

Ironically they've banned a bunch of the genuinely predictive stuff like 'will this town in Ukraine be attacked this week' on public policy grounds.