5.1 bass management

It is useful to have independant control of crossover frequency for all 5 channels even if the speakers are identical since their response is greatly influenced by room placement.

I do agree with most of your analysis but you are suggesting an arrangement that is already a problem since there's no reason to use 100Hz on C and 60 on L/R unless the C is lacking. Phase problems will already exist. Using 100Hz for all is better but too high for me. Small, independant differential adjustments are useful if guided by measurement and careful listening.