“Having listened to the US Constitution and History to 1877 lectures so far, the best I can figure is that the Yazoo land scandal was probably the first step in that direction and the subsequent 14th amendment more explicitly appropriates what was formerly a power of the individual states.”
You answered your own question. Fletcher v. Peck in 1810 was the first instance of a state law being invalidated by the SCOTUS. In fact, John Marshall swore at the VA Ratifying Convention in 1788 that the SCOTUS would never invalidate a State law unless it conflicted with Article 1, Section 10. He lied. The 14th Amendment was not supposed to incorporate the BOR, but it has been argued it did; Madison himself attempted to insert an incorporation amendment into the BOR but he was rejected. Very few members of the founding generation thought it was necessary or wise to have incorporation.
As to your last point, you are also correct, but we are talking baseball and the nationalists are blitzing with their linebackers. I know we have bats, but they wear pads and helmets. With the current de facto unitary construct of the central government, it has become precedence to make everything a national issue. It will take time and perseverance to correct that.