How exactly does "here's a set of rules that people can follow to share resources with minimal problems, it took two decades to figure out" count as a debunking of "sharing resources without an authority to impose rules tends to go badly"?

Your skepticism reflects your naivety. You might want to do your own research into Ostroms Nobel Prize in economics.

> The original Tradgedy of the Commons paper that much modern economic theory rests upon

None of modern economic theory rests upon that paper. Literally the only thing that rests on it is the name of a scenario in game theory, and... it’s not even the dominant name, just an alternate for Prisoner’s Dilemma.

(A lot of social science, and not just economics, applies that scenario, but that doesn’t rest on the paper, but on rational choice theory, or some variation thereon.)

Privatisation is founded upon this (false) conception. In short due to the (false) “unavoidable tragedy of the commons”, our only choice is to have assets either privately owned or owned by the state.

This was what was espoused by the (debunked) paper and remains a pillar of contemporary neo-liberal ideology.

> Privatisation is founded upon this (false) conception

“Privatization” is a government policy, not “modern economic theory”, and to the extent that policy is based on that broad concept of a general effect of which the essay purported to document an example (rather than specific analysis of the domain being privatized), that essay is not the basis (it neither introduced the concept—which was much older—nor was is it the sole purported example).

> This was what was espoused by the (debunked) paper and remains a pillar of contemporary neo-liberal ideology.

It was a pillar of liberal ideology long before the essay was written, it never rested on the essay and, in any case, ideology isn’t the same as economic theory (Austrian school aside.)

Pretty confident that a ‘Nobel Prize in Economics’ fits within ‘Modern economic theory’.

I think we’re at semantics.

> Pretty confident that a ‘Nobel Prize in Economics’ fits within ‘Modern economic theory’.

If you mean the 2009 one for work that included one of the many dismantlings of both the underlying essay you are you are talking about and the broader principal it addresses, sure, but that further rebuts, rather than supports, your argument that modern economic theory is based on that essay.