MOS amplifiers CMRR question
You forgot a big one and in my opinion the main contributor to mismatch ! The threshold voltage Vt !

gm is directly related to Vgt (Vgt = Vgs -Vt) so here you see that a mismatch in Vt also gives a mismatch in Vgt and therefore gm.

Rd is quite unpredictable so it's best to load the differential pair with a low-ohmic load like a mirror input diode or a cascode. That way, Rd doesn't matter much.

But depending on the design and how the transistors are biased things can be completely different ! You cannot say X is always more dominant than Y, because it depends on many other factors !