The same learning rate conclusion is not congruent with reality where anyone can observe that some (smart) peoples learn extremely fast and other ways more slow

The same learning rate conclusion is not congruent with reality where anyone can observe that some (smart) peoples learn extremely fast and other ways more slowly. That is apparent in math, language and practically in any subjects or fields. That can have many reasons. But one strikes to me that the authors could not control the variation in the students population. Obviously, the authors assumed the big number of observations would provide enough variations, but that can be a fallacy. Online learning course can be quite homogenous because they are mostly of choice. People chose them after initial assessment and arguably they will not do so if the course material is too easy or too difficult for them. Another variable the authors could not control is the drop out phenomenon. During an online course, many students will drop out, even half of the initial numbers and that’s a known phenomenon. That can have many reasons as well, for example if they couldn’t keep up with the course or if the course is too easy and could not provide enough value in learning for them. In both cases, the drop out will make the population even more homogeneous. It strikes as odd to me that when encountered with an obvious contradiction to long-held believes (and even common senses), the authors didn’t try to re-examination their assumptions or tried to control the variables (what every researcher should do) but quickly come to a controversial conclusion. From there to extrapolate to the whole mankind and claim every body learns at the same rate, SO the difference in learning outcome MUST BE differences in learning opportunities is not only wrong, it also fraught with ideological agenda, which is the latest thing one should find in a respectable researcher.