IMHO, churning is clearly profitable if you pay off your card every month, will hit the spend requirements organically and are organized enough to cancel to avoid annual fees in the second year. Some people dive into manufactured spending to hit the required spending, but then you really need to consider the time invested.

The question is more about if the rewards are meaningful. I think it's actually worth doing a bit of churning to get exposure to different banks and figure out which one you like... might as well get paid for that. But after a certain point, I value stability and routine more than $300 to jump through hoops... and I'm not going back to Chase no matter what they want to pay me.