I have viewed and explained "layering" as taking the right mix of clothing for the weather one expects to encounter, taking into account abnormal storms/temps and one's own physiology.

I layer differently than my hiking buddies because I generate enormous amounts of heat while walking around even in my everyday life. Whilst hiking I generally wear a wicking tee and have a lightweight long sleeve handy. That long sleeve may be a lightweight merino, or a button down hiking type shirt.

Even ascending 12k ft I am generally in my t shirt and when I "summitted" Humphreys (in AZ) I was in a sleeveless mesh nike shirt. Wasn't cold one bit for the hour plus I was up there. Most everyone around me had on some kind of puffy. I was hot as all git out.

Temps in camp have to get >50 before I am ready for more than a tee.

....just take whatever works for you (lightweight, of course!) and get out there and enjoy yourself... sheesh