First, my comments are not directed to the 744 in particular, but are more general in nature.
The problem with trying to pass off responsibility for specific values of Vmcg/Vmca to one factor only is that there are a number of considerations at play. Some of those, in no particular order, include
(a) flap setting
(b) CG position
(c) thrust output
(d) tyre side force capabilities (Vmcg)
(e) gear layout/geometry (Vmcg)
(f) bank angle (Vmca)
(g) gross weight
(h) differences in empennage flow characteristics on the ground and in flight at much higher alpha in the absence of a ground plane (ie what force can the fin/rudder combination generate ?)
(i) crosswind (Vmcg)
Consideration of lateral tail force arm is relevant to CG and gear/tyre characteristics. Consider also that Vmcg looks at runway centreline divergence while Vmca is concerned with maintaining a flight path.
My observation is that, for many if not all aircraft, Vmcg and Vmca are in the same general ball park .... I have never bothered to worry too much as to which is the higher for a given aircraft.
It is important to keep in mind that the certification figures are based on particular circumstances .. in the real world the actual figures vary, sometimes significantly, from the AFM data ... generally the pilot doesn't have specific data detailing such variations.
Just spent a little time looking over old posts ... Mad (Flt) Scientist's observations in the
following thread provide some additional information ....