and got that early bad ending when Phalanx's Castle suddenly opened up early. Feels like such a weird decision to do that, I had to check GameFAQs on how to progress. I heard similar stories from other players too, did you have any trouble finding all the bits to progress the plot?

I had no issues! I did miss an HP up but i would make note of areas i couldnt get too and tore each level apart hard before moving on. The castle opened for me after i got the 2nd last gem. I may have taken the slow route to get there haha