Tires are cupped. Bad struts or bad alignment?

Brought my Honda Accord 6 months ago. Passenger side rear wheel had hit a curb(before I brought it) and blew the strut.

The cheap dealer only replaced the passenger side rear strut to "make things right". 6 months later(now) I m looking at my tires and I m noticing minor cupping on the inside edge of the DRIVER side rear wheel(side with original strut that wasn t replaced).

I read that it could possibly be alignment that is causing the cupping, or it could be the strut. How do I find out for sure if it s alignment and not strut/vise versa?

Tires are Yokohama Avid Envigors. Car has 45,000 miles. I don t notice any major toe/camber issues with the wheels.

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