At least the first two things you mention (more draw and more spin) could be explained by the smaller diameter -- you may be hitting lower or further off-centre than you expect. Did you ever try something like a Predator Z shaft? If so, were the results different?
I have Z2 shaft and WX900. While I didnt like Z2 because of the lack of feedback I played with WX900 for about 4 years (since its inception to the market, I was one of the very first european players to have it). My WX900 is turned down to about 11.6mm so I am quite used to slim shafts I guess. And while my WX900 is really LD (even lower than Z2 in my opinion) my new solid ash shaft is very close to it in this department. And yes, you are probably right that i can hit the cueball lower but there are shots where i hit the center of the cueball (5-10degree stunshots) and the cueball goes much longer distance than with WX900. Go figure..