You are conflating. The build out is almost entirely for running inference, not training. Open weight models will make that inference build out bet more likely to work as it adds diversity to the suppliers, all the data centers are not beholden to just OAI and Anthropic to buy their compute - they can host their own models (even Chinese ones, in America) if that becomes a popular option.

Zooming out, I think that build out still makes sense. There will be losers in it, but think about how ridiculous the amount of compute we're using has increased from 4 years ago. If I had to guess 60-70% of developers and engineers everywhere in the world are now burning thousands in compute individually every month, whereas it was previously approximately 0.