Yes they do, although I'd be surprised if they fill it every day or even most days. J is notoriously choppy as it doesn't have the price discrimination carriers can use to smooth Y pax around to fill up the days. Simultaneously its strength and its weakness from an airline revenue perspective. Singapore has tried and failed in this product before; maybe this time the market is ready - still, it's probably not the license to print money one might imagine.

I think quite a few financial/corporate centre city pairs support a business-only flight, though even with this famously rich city pair, BA1 from london city to NY is flown on an a320! It's a difficult product to make work.

Upon further reflection I believe what the grandparent commenter was trying to say is that airlines, as a whole, get more revenue from economy pax, which is probably true for most airlines. On a route that supports a decent J component, though, they can rake in the cash.

Business and premium economy