(1) As an expert in scientific discovery in the 19th and 20th century, let's disassemble a general claim using the specific example of Einstein's work on special relativity and general relativity. First, here is the claim: "If I give you two PhD students, one who completed their thesis in two years and one who took eight years… you can be almost certain that the two-year thesis will be much better." Things to keep in mind: (1) special relativity was baked into Maxwell's electromagnetism and should have been discovered years before Einstein, and (2) general relativity was a novel application of non-Euclidean geometry and mathematics to the gravity problem, that is the acceleration problem, and was quite a unique accomplishment. Discuss the 'amount of research' that went into each development by Einstein and lay out the argument that this disproves our claim, with any caveats you think appropriate.
(2) In general, it seems to take about ten years of diligent focused effort for a person to develop their skill levels to the point where they can make meaningful contributions to any science, engineering, or even artistic field. Einstein seems to follow this trend, if we start counting from his teenage fascination with physics. Another example is the very popular instructional videos on machine learning by Andrej Karpathy, eg "The spelled out intro to neural networks and backpropagation: building micrograd" in which he begins by stating he's been programming neural nets for ten years. Thus, it seems fair to conclude that 'move fast' only makes sense after 'develop the required expertise to know how to move fast'.