We have no good theory of mass scale for fermions. The masses of the fermions would make a little more sense if we were missing the partner to the strange quark. The charm quark would happily be a third generation quark along with the bottom quark. The top quark might then be the first member of
the fourth generation of quarks or perhaps it would switch places with charm.
Generations of matter
Type First Second Third
-1 electron muon tau
mass 0.511 MeV 106 MeV 1777 MeV
+2/3 up top charm
mass 2 MeV 172000 MeV 1270 MeV
-1/3 down strange bottom
mass 4.2 MeV 100 MeV 4200 MeV
0 electron neutrino muon neutrino tau neutrino
mass < 10-6 MeV < 0.17 MeV < 15 MeV