Is the Oral Law a Good Idea?

From a purely pragmatic perspective, is it a good idea to have a large body of vital law and principles committed to memory and not to writing?

The believers in the oral law claim that an Oral law was given to Moses and not written down. They then argue that it was transmitted /taught orally for another 1500 years or so.  The excuse they give for it to be written down is:

"In the lifetime of Rabbi Yehuda Hanasi (around 1700 years ago), Roman persecution, the recent destruction of the second Temple and the disruption of stable Jewish community life threatened our ability to properly retain and transmit this oral law. Rabbi Yehuda, therefore, wrote down the bare basics in the Mishna. A couple of centuries of hardship and persecution later, the rabbis of Babylonia saw a need to record even more detail and compiled a written version of what is known as the Talmud"

https://torah.org/learning/basics-primer-torah-oraltorah/

It seems to be a very inefficient  system and design.  Why would this section be given in oral form originally, if it was inevitable for it to be written down?
And what is unique about the the hardship of Roman persecution?  There was persecution even before the Romans, and there was the destruction of the First Temple. In First Temple times, there were many periods of idolatry, when even the Written law was lost or forgotten. how could the oral law be remembered then?  And if it existed, why wasn't it written down in those times?

So the form of oral transmission is really not a good idea. it is impossible to verbally remember a mass of information the size of the Talmud.  If there was no written format, then even a photographic memory would not suffice.  So it follows that not only is it a bad idea, it was impossible to implement.