It's more like you offering to invest $1bn in Fred's company in return for a promise to spend $1bn for sink fixing services. You could question if there is a demand or $1bn of sink fixing in the same way that you could wonder about the demand for $100bn of AI slop.

Investing is just an equivalent value exchange. My point is that while you could say in my example that money just moved around in a circle, it turns out that money moving around in a circle is actually fine.

I agree money in a circle is fine. But in your example there is a straightforward situation of an end customer paying money for a service, eg. getting a sink fixed. The worry with the data centers is will there be enough end customers willing to pay what the data centers cost.

No, the problem here would be we don't know if anybody actually need wifi, a shed or his sink to be repaired.

We do, because they've already done that stuff. You're talking about whether any of the 3 people will be able to get more money in afterwards, which seems like a separate issue to this.