Does eating hard food really cause wisdom teeth to erupt properly?
Yes

The relative size and robustness of the jaw does appear to be strongly affected by diet, significantly more so than other parts of the skull. This is not that surprising many developmental pathways interact with physical activity. Bones in particular often rely on a certain amount of stress to develop properly. It is not all that different from low scale bone atrophy.  

Size of the jaw of course effects how much space there is for wisdom teeth. As for the evolutionary effect, consider we have only had access to soft processed food on any scale in the last few generation, that is not much time evolutionarily. 

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