I think it is not easy or not necessary to compare MK with BS. Yes, both were born in 1949, and both of them are well respected artists in the music-community and both persons buildt their musical legends in their lifetime.
OK, picture this, in the mid-eighties, Bruce was a really athletic type of man, no question and MK was more tall and slim, not so really athletic like Bruce. Getting older is also an individual process, like their personas or their lived carreers as celebrities.
Just my two cents to this topic.