Yes, there are occasional complaints about this. The problem is that the costs you are seeing are a bit notional: they aren't the actual costs of the legs, they smooth out the cost differences between the outbound and inbound. If you change the outbound then there is a recalculation which then causes the problem you describe.

I agree that the EK grid (and indeed many other airlines do the same) is a lot simpler for frequent flyers, the BA system is probably better, or at least simpler, for someone with a relatively fixed travel plan.

As someone who goes through this booking process pretty much daily, it's just a case of getting used to it. Eventually you don't really notice it. If you want the cheapest possible dates, use ITA Matrix, or go via Find Our Lowest Fares.