To see if that is too much or not, we have to put that number in relation to the value those datacenters will create in the future.
If global GDP is $100T and labor is 50% of that, then the current TAM for intelligence is around $50T.
How much of that has to be automated per year to justify $400B of investment? For a 10% ROI it would be around 1%, right? But the datacenters will not be the only cost of generating artificial work. We also need energy, software and robots. So let's say 2%.
So it comes down to the question whether those datacenters built for $400B will automate 2% of global GDP in the foreseeable future.
And there is another option: That the TAM increases. That we use the new possibilities we have to build more products and services. And see global GDP grow. 2% AI driven global GDP growth would also justify the $400B datacenter buildout.
So let's think about a mix: 1% labor automation and 1% GDP growth per year via AI. That would be needed to justify continued spending of $400B per year for the AI buildout.