In my program, we had a saying that lowbrow philosophers end every argument with "Plato said it first"; middlebrows say "Kant said it first"; highbrows say "Wittgenstein said it first."

Modern philosophy hasn't "obviated" Plato, per se, but any competent philosopher today can discuss what Plato thought generally and how/why we think differently today. The philosophical method of analysis and argument remains, but no one talks seriously about Platonic forms except as part of the history.

It seems to me quite a tall order to say that "any competent philosopher today can discuss what Plato thought generally and how/why we think differently today."

Do you have a summary or link to one?

When I say "any competent philosopher", I'm being specific to the Western philosophical tradition. Up through the 19th century, any education in philosophy, classics, or the humanities was virtually certain to include reading Plato; since then, more organized philosophy degrees in university always have some ancient philosophy requirement that includes Plato/Aristotle. Additionally, Plato is frequently used as introductory material in philosophy classes to demonstrate how it works via the Socratic method. Within the confines of "professional" philosophy today, it's almost impossible not to have a basic grasp of Plato.

As for how and why we think differently today: any study of the history of philosophy is partly the study of refuting earlier philosophers. If you're aware of Plato, you're aware of criticisms of Plato and how that formed the basis of other ideas.

With some exceptions. Mathematical Platonism is still taken quite seriously, though it's evolved a bit since the Meno.

Interesting. How's Intuitionism doing?

Intuitionism/constructivism has gained much momentum in recent years.

It is the foundation for Hawking’s model-dependent realism [1]; or more radically Dummett’s anti-realism [2].

Speaking purely about Mathematics - there have been great strides in constructive mathematics in the last 3-4 decades, and great overlaps with computer science (Curry-Howard-Lambek correspondence). A formalist might even say that the fields of logic, mathematics and computer science are identical.

1. https://en.wikipedia.org/wiki/Model-dependent_realism

2. https://en.wikipedia.org/wiki/Anti-realism

>But the point of learning about Pythagoreanism isn't to learn ancient history. It is to learn philosophy.

The two, at least according to Hegel, are not so easily separable.

"The more the ordinary mind takes the opposition between true and false to be fixed, the more is it accustomed to expect either agreement or contradiction with a given philosophical system, and only to see reason for the one or the other in any explanatory statement concerning such a system. It does not conceive the diversity of philosophical systems as the progressive evolution of truth; rather, it sees only contradiction in that variety. The bud disappears when the blossom breaks through, and we might say that the former is refuted by the latter; in the same way when the fruit comes, the blossom may be explained to be a false form of the plant’s existence, for the fruit appears as its true nature in place of the blossom. These stages are not merely differentiated; they supplant one another as being incompatible with one another. But the ceaseless activity of their own inherent nature makes them at the same time moments of an organic unity, where they not merely do not contradict one another, but where one is as necessary as the other; and this equal necessity of all moments constitutes alone and thereby the life of the whole."

The legacy isn't avoided in upper level classes. And an intro survey in philosophy will cover it. But if I am in an upper level course on contemporary philosophy, I don't need to rehash Platonism. I know philosophy is said to be a series of footnotes to Plato, but this isn't literally the case.

You wouldn't start a Tudor England history course with the Roman Empire just because they had historical influence. You'd probably be aware of the linking via the introductory courses.

Not every course needs to discuss every facet of a topic, foundational or not.