actually, both hands have like almost similar muscles.. it is just a matter of unlocking your left hand... like keep practicing until you feel your wrist loosen. to do that your left hand must do what your right hand can do.
i thought of something that i don't know if it helps, but like all the patterns that the hand does uses a different muscle, and all these muscles will sum up to the speed of your single stroke. such patterns are like the moellar motion, single strokes, double strokes, triple strokes, 4 strokes, different rock patterns ( eg 1e&, 1 &a), diddle patterns ( r rr, l ll), flam patterns, samba patterns... if your left hand can play all these things, one day it will loosen up and be really speed up
i guess that is why rudiments are so impt...
leading with the left hand thing helps too, but it is more in the mind.... as most things are in the mind
at least it happened to me so yeah i think since we all have similar hands and a drummer's feel for music, it should work for you too
try?
keep going man, we are all working on this