A Tesla focused Youtuber recently did a video [1] where he accessed some of the data on the CAN bus, and it showed excellent balancing between the cells. The highest voltage cell reported 3.87V, with the lowest voltage cell reporting 3.864V. So the highest voltage cell has only a 0.1% higher voltage than the lowest. That's in the middle of a discharge cycle, so this may not be representative of the real capacity difference of each cell, but they're being discharging in a very balanced manner. I don't work with batteries often, so take my analysis with a grain of salt, but it seems to me that (the lack of) battery degradation is one of Tesla's biggest strengths when it comes to their battery technology.