I think the difference is that Mass scripture reading is part of the greater, a supplement to, and the Mass itself is scripture. Also, the homily on the scripture is not the Mass.
When I attended Protestant churches, the homily, sermon, is the crux of the service, and it is mostly Bible study, since they do not have Mass. They’re gathered to hear someone preach - about the Bible. It’s the sola scriptura thing again.
The majority of my scripture reading is outside Mass, often selected by what was included in the Mass. The value of scripture in Mass, to me, is providing the proper context and interpretation - a guide for my reading outside Mass.
I’m glad we have a lot of Scripture at Mass but any way you look at it, it’s that Meal that’s at the center of it and the main reason we go.