i don't really think it is the multi - basically i play hybrids with mainly shaped polys and the mcs as cross most of the time and i do develop with this set-up considerable spin. i did try some fullbed polys and there was not more spin as compared to the hybrids.
i'm sure that the multi basically prevented the kevlar from sliding and a poly as a cross would have allowed for less friction, but i doubt that i would have liked the feeling of such a combination. in my young years i played very high tensions - 32kg in wooden sticks - but that was with gut. so it's not so much the stiffness of the stringbed that put me off, it's more the lack of response.