I can definitely understand the feeling of wasted time, and perhaps I didn't do a good job of explaining the point.

The main issue is that you shouldn't discuss your current salary, but you should absolutely discuss the budget for the role. The reasons I make the distinction is because many candidates will have a lower current salary, and although the company has budgeted X for the role they will be happy to pay (X-delta) instead.

Talking about your current salary is basically never a good idea, but talking about the budget and salary for the role is certainly a good idea.