True.

Passing tech is the minimal accepted cage structure. Rarely is it adequate or sufficient for improving the car. And there's typically plenty of room for improvement of driver safety.

Safety is a given. We see people walk away from things like hitting the wall at high speed and the Stevie Jackson blow-over. Rarely these days do we see a tube car chassis/cab structure compromised. The structure is stiff and strong. Rule changes usually result from some unusual situation that we don't want to have happen again. The idea is to contain the driver in that protective structure. Recent improvements have been in driver gear - helmets, HANS, padding, shields, restraints. There is such a thing as an unsurvivable wreck. The body can only take so much G-force.

Chassis response/flex or the lack of it, is by design. Added or reduced tubing and tube sizing, bracing, diagonals, slip joints, while maintaining the requirements of the spec, can be used. Proper bracing is a more effective way of stiffening the structure. While they could, I don't know of anyone who uses 1.75" in place of 1.625".