Look at China. They have built about a dozen cities where nobody lives. All that spending goes to GDP but adds no real wealth.
government spending is a net negative to the economy, it sucks out investment in the real economy. Government is so inefficient that it couldn’t do anything else.
GDP is another invention of the Keynesians. It measures consumer and, as you said, government spending. It completely ignores business-to-business spending which is larger than consumer spending.
That 70% of the US economy is dependent on consumer spending is a complete falsehood -- it's more like 30% or 35%.
Why? Because the Keynesians claim that economic growth consists in more spending -- not investment. Dumb and wrong.