sounds to me like you have some counterfeit denso plugs
Yep, or some major engine defect or malfunction. Denso along with NGK make well-made spark plugs. The iridium ones in my old Sienna, ECHO and BMW look very good even after 100,000 miles. If his were worn down to nubs after 35,000 miles then either they are fake or there is something else going on.