Taxes are levied on all kinds of things that are not economic activity. Including, in Norway, on ownership.

> Count the number of companies created and grown in the last 20 years and see the trend. If it's going down your tax revenues will decrease. So indeed number of companies created is a very good proxy for future tax revenues.

Even if it was that simple, that does not provide even a correlation - much less causation - with wealth taxes, which Norway has had for decades. E.g. we'd expect to see changes corresponding with changes in the wealth tax rates.