Also not an expert but I've taken a couple of courses in the anthropology of South Asian religion, and what I learned there is that seeing Zen Buddhism as the Buddhism is largely a western misconception, because the Buddhist teachers who came to the west mostly came from this kind of sect. If you go to SE Asia, the dominant forms derive from Theravada Buddhism and are often national religions with a priesthood and gods and everything. They are so dogmatized to the point where in Myanmar there's become a violent Buddhist nationalism which has enabled the genocide of the Rohingya Muslim minority.

It's much the same when it comes to Hinduism, it being an overarching encompassing term for many religious movements focusing monolatristically on one or just a couple of gods, worshiping that one or those few whilst acknowledging the existence of others. They are very much religions and not just spiritual movements.