Explaining Poorly Chosen Major and Average Grades
I do think you should explain your mediocre grades in your major in your application.  Give the honest truth that you feel it was a poor choice of major and you lacked interest in the subject.  It's not perfect, but it's better than no explanation.

The more you can portray it as a story of growing and maturing over time, the better.  Focus on the positive: lessons learned, developing more discipline, finding your passion in your physics classes, etc.

I don't think you should say you were "viciously lured" into engineering.  It doesn't really add anything to the story, and also it comes across as blame-shifting.