Totally agree. That doesn't mean it can't generate massive ROI.
> Govt investment would also drive the cost of GPUs up a great deal
Difficult to say this ex ante. On its own, yes. But it would displace some demand. And it could help boost chip production in the long run.
> Not sure why a publicly accessible GPU cluster would be a better solution than the current system of research grants
Those receiving the grants have to pay a private owner of the GPUs. That gatekeeping might be both problematic, if there is a conflict of interests, and inefficient. (Consider why the government runs its own supercomputers versus contracting everything to Oracle and IBM.)