Opinions, everyone's got one!
Try looking at the situation logically, putting aside your own opinion for a moment. If Flights of Passage was over rated wouldn't the lines have died down by now? Would people still be lining up for hours to ride it, and then getting back in line to wait hours to ride it again? Would people be struggling to get Fastpasses? The ride has enormous capacity!
Most nights, by park close, Navi River Journey is either a walk on or close to it. The other headliners (Safari, Everest) are incredibly easy to get into.
If, all these months later, people are
still losing their minds over FoP, the ride is clearly not over rated.
Obviously it won't be everyone's cup of tea. And if you found it underwhelming, there's nothing wrong with that. But conversely, everyone else who was blown away by the experience is equally "correct" in their opinion of the ride. It can't be "over rated". It's rated exactly how people rate it, and if the majority rates it higher than you would, that's their right.
Personally, I think the ride is gorgeous, and on my third go through I took my eyes off the screen and had a look around at the ride mechanism. Amazing! I like it much better than New Soarin', where the distortions and Uncanny Valley critters bug me slightly. As for Journey... it's showing its age in comparison to FoP, being less immersive with more jarring scene changes and less convincing animations, though the ride itself is definitely more thrilling (and nausea-inducing). I love Journey slightly more, only because Harry Potter resonates more with me than Avatar. But I feel like FoP is a technologically superior ride (especially since they've fixed the headgear).