Those who cannot remember the past are condemned to repeat it. – George Santayana, The Life of Reason, 1905.
But history is not philosophy, so the implicit premise, which boils down to, "history is not necessary to philosophy," is wrong-headed, but it is also assuming the conclusion, which is question begging.
History is important to history, understanding how events in the past caused things to be the way they are today. Further, the history of philosophy is not identical to the philosophy in history just as the history of technology is not itself technology. When studying Ancient Philosophy one is not studying the history of ancient philosophy, but the ancient philosophy itself. Conversely, studying history of philosophy is not philosophical study, it is instead studying history, focusing on when and who said in what circumstances, and is not primarily concerned with understanding what was said.
Read page 9 in the PDF again - the author goes to good lengths to grapple with this argument and why it is not correct. In particular:
In order to repeat the mistakes of a famous philosopher, one must first
share their beliefs. Now, few people are born with any degree of credence
in the far-fetched propositions embraced by many philosophers. In general,
these kinds of beliefs have to be acquired; and the only way of acquiring
them is to study these authors. It seems that if we wanted to avoid acquir-
ing false beliefs that we would never arrive at except by reading a particu-
lar author, the best thing by far we could do is to avoid reading that
author.Incidentally, how's the Bohr model doing? Still widely taught? Well why's that, since it's wrong?
In practice it fails on multiple grounds:
First, it's not possible to censor all instances of such philosophical works. The historical record is filled with attempts to do so. These can be somewhat successful, and there are in fact philosophers whose names reach us only by reputation, citation, or other mention, but some philosophy has leaked through.
Secondly, a fresh attempt at doing so would amount to one of the most jarring cases of oppressive authoritarian censorship in all history.
Thirdly, the ideas have come to permeate modern culture. One of the joys of reading philosophy (or literature) is recognising the original source of a specific phrase or concept. I can recall one of my own uni lit courses in which we read Tennyson's "In Memoriam A.H.H.", and came across the stanza:
I hold it true, whate'er befall;
I feel it, when I sorrow most;
'Tis better to have loved and lost
Than never to have loved at all.
A woman in the class exclaimed "Oh, that's where 'Tis better to have loved and lost' comes from?". I'm sure that was a bright day for the lecturer.
Encounters with philosophical history are similar, though often what strikes me is the nuance and context in which even well-known concepts are grounded (say: Pascal's wager, which is far more about expected returns than belief of God's existence).
Fourth, bad ideas seem highly susceptible to arising again and again due to their very simplicity and appeal. This might of course be affected by the third factor, but independent (or at least very distantly related) instances of similar tropes appearing in mythology and sagas suggest that there are ideas which are simply either infinitely regenerative as with Prometheus's liver, or which resist all attempts to kill them, where two new myths grow back for each one that's cut off, as with the hydra's heads.
(Even mythical stories can serve as useful illustrations, itself a factor in their longevity.)
By going back to fallacious reasoning or conclusions and looking at how the ideas emerged, were adopted, and often explicitly encouraged we can obtain, I'd think, a better understanding of similar such processes in our own time. The divorce of ancient beliefs from current tribalism, politics, and passions serves this purpose all the better, though it does help to consider the ancients not as childlike innocents and naifs or ourselves as beyond their own failings when doing so.
And the trove of ancient philosophy is large enough that a specialisation in its history is required such that mere mortals may benefit from its findings, classifications, and synthesis.