I don't think it's all that complex. As intended, the NY families perceived the Corleones as weak and vulnerable. As a hugely experienced Don, Vito could figure on a probable scenario. I don't think Vito was particularly prescient about it. If at the height of Corleone power, Sollozzo felt comfortable making a move against the Corleones, why not make a move now that the Corleones were at the perceived nadir of power.