I think many of us use whatever our first "instructor/teacher" told us to use.

You're exactly right. That's where I was told to use cotton.

Some of my work shirts and most of hubby's are cotton with polyester serger thread. The fabric will wear out near the seam but the seam will live forever! Look at some of your cotton shirts & blouses, especially the ones that get washed a lot. The fabric will give out before the thread does so use whatever works for you.

I used a lot of poly when I started quilting. Those quilts are holding up just fine.