Happy to be proved wrong! As I said I'm not an expert. But some authoritative links would be helpful, as what you're saying clashes with pretty much everything I've read over the last 18 months - not suggesting the testing apparatus was constructed out of nothing, only that it posed challenges specific to the virus, likewise the scaling of the testing as a national infrastructure
I expect the challenges you've read about will mention are all to do with scaling things up and perhaps other details such as the time window when a particular infected person will be most likely to generate a sample that allows the virus to be detected. If you have one that describes other problems that make a mockery of what I've been saying, then I would very much like to read it.
It isnt easy for me to point to a single article which demonstrates to your satisfaction that other problems were not a big deal with this sort of testing. I will try to find something. My first attempt resulted in too many fragments of info from different articles and my reply became a giant mess which I have decided to throw away.
For example a proper guide would include the history of PCR stuff (over 35 years old now), the number of things its been used for historically with great results, and more recent applications of this technology, the estimated size of the market pre-pandemic (4.5 billion dollars by some accounts in 2019), some stories about how quickly the assays were created to enable the pandemic virus to be detected via this approach.
Since it is a well established and standardised form of testing, one which had a large and expending industry and range of uses behind it well before this pandemic, I really require some concrete example of what sort of other issue with it you think existed in regards this pandemic. I dont even know what sort of problems you mean, this is fairly mature technology and the current virus has more than enough in common with SARS and MERS that we knew some ways to detect it from the start. Once details of the virus were available, it was a pretty safe bet that suitable PCR assays could be developed very rapidly.
How quickly it was successfully adopted by nations should really be the main proof of what Im saying, humanity really hit the ground running in this respect, we didnt have to wait for any new advances in technology, we didnt get stuck for months waiting for some tricky technical problems to be solved. We did have to wait for all the logistics to fall into place. All the major challenges were in scaling capacity up, and there are an incredible number of uses for this sort of testing that could have given us reasons to scale up long before this pandemic arrived. In fact all the other uses of this sort of testing are one of the big reasons we did actually manage to scale up in the first year, because there was lots of capacity sitting around for use in other work, and it was more a question of organising these disparate resources into a cohesive network, and getting enough supply of consumables, than really starting from almost nothing.