As topics become more sophisticated, the time to competency and insight increases.
Someone for instance, truly committed to studying the entire corpus of thoughts on political economy, from the Frankfurt school, Chicago school, Stockholm school, Austrian school, Keynsianism, Marxian, Monetarism, New Classical, Public Choice, Georgism, Bachuninism... Each of those are hard and complicated. A sincere dedicated study of all of them would likely take decades.
If you had 300 years then not only could you do that, but you could also make meaningful contributions to the field.
Imagine public policy by people who were able to dedicate 100 years to its study.
50 or 100 year studies which currently have to be chaperoned across multiple generations of researchers could be done by a single team.
The accumulated wisdom that manifests itself in the written word would be far more potent with centuries of accumulations. In a way, genius is a measure of speed and time, the quickness of ones assimilation of the topic. With enough time, the plane of genius might be accessible to nearly all.
Other, much longer efforts would be engaged with more frequently. For instance, The art of computer programming, started 51 years ago, would be one amongst a much larger number of works of similar breadth, if taking a century to complete something was feasible for all.
The differences this would manifest would be likely as stark as if someone from the 18th century descended upon a modern urban metropolis.