I'm not convinced by the author's argument. The difference between philosophy and physics is that
old philosophical arguments do not become less correct over time. In physics, later physicists build on the earlier body of knowledge and refine it, making it more correct. In philosophy, later philosophers may suggest a counterargument to the early philosopher, but as philosophy does not normally deal in absolutes it is impossible to say the later philosopher is now more correct and worth reading instead of the earlier philosopher.
For example: a philosopher may argue that murder is morally wrong, and a later philosopher may argue that murder is morally right. Neither answer is factually wrong or right. We should therefore read the work of both philosophers to get the most value out of our studies and to form our own opinions.
---
I'd also argue that it's not always worth reading the earlier philosopher's work if someone else can rewrite it in a better form. Personally I think Immanuel Kant's philosophy is interesting but poorly written, and you'd get more value out of reading a later text about his philosophy that his works himself.
Other writers such as Plato have stood the test of time and are worth reading (assuming you have a good translation).
For example: a philosopher may argue that murder is morally wrong, and a later philosopher may argue that murder is morally right. Neither answer is factually wrong or right. We should therefore read the work of both philosophers to get the most value out of our studies and to form our own opinions.
---
I'd also argue that it's not always worth reading the earlier philosopher's work if someone else can rewrite it in a better form. Personally I think Immanuel Kant's philosophy is interesting but poorly written, and you'd get more value out of reading a later text about his philosophy that his works himself.
Other writers such as Plato have stood the test of time and are worth reading (assuming you have a good translation).