Yes. Shining and Cadence were relatively vital to the story, at least for the first third anyways. But then they sort of got thrown to the wayside after their initial part in the story was done. 

The CMC’s role in the film actually intertwined with Shining and Cadence’s. At some point, the kids accidentally get caught up in the whole mess when going on a field-trip that happens to be taking place in Canterlot. When they go off on their own, they find themselves in the Canterlot dungeon (ala “The Goonies”) and its there that they find out about what Discord is planning and what he intends to do with Twilight.

So from there, the kids help Shining and Cadence escape so that they can get outside of the city to help in the search for Twilight. Again, it just sort of made things get out of hand as to why it was cut. But for the first third, we really had to think hard about how things were going to be changed. But luckily, we found a way to make it work.