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.
Do you have a summary or link to one?
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.
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.
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."
Not every course needs to discuss every facet of a topic, foundational or not.
1. Oneness 2. "all is number" 3. There are fundamental harmonies in the cosmos and the soul 4. Integration of the rational and the spiritual
It's philosophy as a scientific religious pursuit. I don't think that comes up much in philosophy 101
But as for courses dealing with presocratic philosophy, history of ancient Greek philosophy, mathematic and science ... They most certainly do exist and deal with exactly this legacy.