Author's main idea is that knowledge is not always cumulative, sometimes new ideas disrupts and replaces old ones, and in some cases, even reduce the burden because it is also simpler.

The problem is that most new ideas are, in fact, cumulative, and hence increases the burden at a faster rate than disruptive ideas reduce it

The idea of "Burden of knowledge" only requires that most knowledge accumulates. The fact that there are exceptions that do not accumulate does not disprove it