To be fair, the real issue with the Pandora boat ride isn't what comes before the Shaman... it's what comes after.
Had you actually 'arrived' wherever you were going after the Shaman (i.e. the soul tree with some animals and Navi hanging around it in a large open air room), the ride would probably be well received. It's too short.
Instead the ride builds to the Shaman and it seems like she just is like ok ride over, you can't go to the sacred place, baaiii.
Almost every instance of one impressive AA doesn't have the AA be the finale. Everest still has coaster elements. JTTCOE has the thrill. Roaring Rapids basically still has a ton of rapids left to go. Navi River Journey just confusingly ends.
After people have waited 75 minutes for a C-ticket.
I kind of feel the same about Mermaid. Had we entered a finale show room with Eric sailing into oversized cackling Ursula, it wouldn't feel like it ended with a wet fart.