[Maken]

You are right, not all the temples in the "line" are cathedrals, which does make the entire story less credible.

[jfengel]

"Cathedral" is a very specific kind of church, but not necessarily all that significant. It's where they happened to have centered a local bishopric. (A cathedra is a chair, specifically one that a bishop sits in.)

So there are a lot of magnificent churches that aren't cathedrals (Sagrada Familia, Westminster Abbey, St. Peter's in the Vatican), and a lot of cathedrals that are actually rather dull architecturally.

[Maken]

Precisely cathedrals are rare enough that seven of them in a line dedicated to the same archangel could no be a coincidence. I bet you can make similar lines if you look for churchess and sanctuaries dedicated to another important saint or saintess.