OK, OK. I don't have my engineering references handy, so I'll have to work from memory. How do you know the strut towers don't flex in opposite directions? You'd need a dial indicator and some kind of recorder to track the movement during hard cornering. Or maybe strap a friend in the trunk to watch! Cornering loads are primarily torsion, so unless the chassis is extremely stiff there will be different forces acting on each side of the car. One strut tower will be moving one way while the other is not. Outside tire heavily loaded, inside hardly at all.
On the subject of AL vs. steel... Name 1 space frame race car chassis fabricated from aluminum. It was done once, but shelved for the reasons outlined as follows. No-one uses aluminum tube for chassis/structural applications because of fatigue. AL work fatigues, especially bad if it's been welded. Every time you put your car through some kind of structural stress (hard cornering), the material gets a little weaker until 1 day.... AL must be 40% thicker (wall or OD) to have equal strength to steel. Then there's the problem of anodic corrosion where the AL and ferrous meet. Plus, all the AL braces are bolt-on. Another drawback to ultimate strength.
