Those are really good points. I sometimes wonder myself. If you ask me, WWOHP still looks very busy and very popular even now, two + years later, and I will still often see over 100+ minute waits for FJ during peak days.
IMO, it seems relatively low because, compared to Florida, the opening days didn't have overflow crowds of people where timed entry into the land was required--which I think nearly everyone was expecting (like I'm expecting for GE at Disneyland). When you expect masses of humanity, traffic jams, people camping out, timed entry, etc, and none of that ends up happening, many people jumped to the conclusion the land underperformed.
But as far as I can tell (and I have no actual data, just based on my own observations of visiting the park about every 2-3 weeks since WWOHP has opened), the land is drawing people in, and consistently, too. So I think what everyone though would be an explosion has turned out to be a slow, but very consistent, burn.