If its that bad it should be pretty easy to see metal to metal contact. Pull the wheels off and look on inside of rim and throughout wheel well. Using a light might make it easier to spot fresh metal being nice and shiny. And yes your offset can cause issues.
Also, I have put thousands of tires on in my life/career and used just an impact (after starting lug nuts by hand). I'm not saying there's not a torque rating and using an impact is the 100% correct way to do. I'm saying I have done it (just like you did) and never had an issue.