I'm obviously using the archetype of Leibniz here as an example but pick your favorite polymath.
I was replying to “even the known knowledge is extremely hard for talented university students to learn”. If complexity of the known knowledge one must learn to substantially contribute is the reason becoming an accomplished multidisciplinary is impossible nowadays, then it sounds like we could use some better models and levels of abstraction.
JVM was one of the smartest ever, but Euler was there centuries before and shows up in so many places.
If I had a Time Machine I'd love to get those two together for a stiff drink and a banter.
https://youtu.be/Oh31I1F2vds?t=189 Describes Von Neumann's final days struggle when he couldn't think. Thinking, an activity which he loved the most.