No, it is simply rational to measure results higher than intentions. Transnet's failures are provably NOT because of the EXISTENCE of transnet - but because of incorrect management, bad rules or other fixable problems.
If it was impossible for a there to BE a public good in a form such as that then the BBC could not exist - let alone be arguably the very best in the world at what they do and providing the people who fund it with a service that leaves every competitor (including an entire multi-billion dollar private industry) in the dust in terms of quality, cost and convenience.

It is possible to have a public service that actually serves the public good - it can and has been done many times. When a public service fails to do so - that is not proof that public service isn't a viable option (if it was- there would be no successes) - it's proof that this particular public service has implementation flaws which must be fixed.