Does the conclusion hold for overweight people? While I was sub-80kg my sneakers used to last years. Once I passed the 100kg threshold I noticed my sneakers get worn-out after ~6 months, just walking. Makes me afraid the same happens to my knees.

Is there any distinction made between trail and road runs?

I don't know how you can claim that running on hard pavement is good for the body, with comparable cardio as a control.

I strongly doubt that this control model is correct if the recommended adjustment is to discard the association between e.g. patellar tendinitis and patellofemoral pain syndrome and running surface hardness. Still, the guidelines should be to avoid road runs because they certainly exacerbate symptoms of such injuries or disorders.