[RandomLensman]

GDP is always an "estimate", not sure what your issue is. What specifically do you dislike about this estimate?

Physics isn't "complete nonsense" just because we don't know the exact mass of a proton but rather have some small uncertainty there.

[flakeoil]

The main problem is that GDP can and is defined in so many different ways and massaged and changed to anyones liking.

Same with inflation. It's hard to measure correctly in the first place and becomes even more useless as it is defined differently at every occasion or when it does not match whatever one tries to achieve.

[RandomLensman]

Any forecast of GDP or inflation is then nonsense by definition as the numbers are meaningless?

[flakeoil]

Yes, that's right. Just look at the clueless central banks.