Hmm - Zone 3 is along the Nortern tier of US, correct? What do your neighbors lawns look like right now? What are your lawn care practices in the way of summer irrigation, spring & fall fertilizing & spring overseeding? And, are the bare spots high spots in ground level or is your lawn very flat & even?

What kind of grass did you plant?

Where do you live? The Zone is not always helpful, because it says nothing about the soil or the climate (except winter cold).

Whatever it needs, dethatching is NOT one of them. It's already thin.

You seeded 2 years ago. Did you not seed again last fall?

The soil looks like sand. If it is, then you will never need to aerate. If it is just gray soil, it might need to be aerated some day.

When were the last two times you fertilized? And what did you use? Have you used any herbicides, insecticides, or fungicides in the past 2 years? If so, what and when?