No, belmont, it isn't. You literally don't know what you're talking about.
the Metroidvania set-up is hardly designed for plot embracement and it is not easy to write up, expound upon and deal with a cut-scene based storyline which is almost required in this day and age due to it's design. Have you ever noticed that in AoS and PoR, etc., practically all the cutscenes consist of randomly finding a character and interacting with them for a few minutes before running along on your way?
Christ. It has little to do with IGA, and everything to do with the medium. Curse of Darkness's storyline was much better and was actually executed well, and this is mostly due to its medium.
Order of ecclesia, which by far had the best story and plot presentation thus far, was only able to do so because of the fact that they broke away from the strictly metroidvania mold.
I have no issues stating that in my experience out of all the genres i've worked with, the metroidvania genre as utilized by Super Metroid and a majority of the Castlevania games is by far the hardest to implement a good story in. It simply is not designed for it.