VMCG is demonstrated at close to zero angle of attack.
VMCA is demonstrated at as low a speed as possible IN-AIR, and thus at as high an angle of attack as can be achieved.
VMCG is a dynamic manoeuvre, initiated from close to zero angle of sideslip
VMCA is principally a static manoeuvre, demonstrated with significant sideslip.
Consider ... in how many other cases would you seek to compare a low-alpha, low-beta, dynamic condition with a high-alpha, high-sideslip, static condition and expect to find any particular relationship?
Add to those details that both are demonstrated conditions and not analyzed in most cases, and it's clear that there should be no expectation of one being greater or lower than the other...