Hi,
I am quite new in the EMC field.
I think the return path is fine for the desired signal in your case.
But the return path for any RF noise signal superimposed on this signal is bad because it is the same. Let me explain.
This RF noise signal should use the plane just beneath, irrespective if it is ground of power: at RF, the noise can go through decoupling capacitors and change plane easily. In your stackup, the RF noise should return on layer 2 which is split and thus goes through layer 3 which is further away from layer 1 meaning higher inductance, radiated field etc.
The solution here would be to route on layer 4 because the plane just above is not split.
You can see the RF current path in the figure below.
There's also the skin effect which prevents the RF current to cross a plane. The current then has to follow the outer surfaces...
I recommend you "split ground/power planes" section from the great book of Henry W. Ott : "Electromagnetic Compatibility Engineering".