However, it's possible that the flexibility of the settings toward other cases (like using the router with older hardware, or less compatible or buggy devices) necessitate their presence and complexity. Seems likely to me that each of these settings has been placed due to a specific support case with the plethora of device data and testing cases that they must have from years of customer support.

I think, then, that the settings are not for the maximal optimal case, and the misunderstanding here is that the router is somehow not initialized for maximum performance. This may be true for other router brands, but in my experience, is not true for Apple.