I also was surprised that they took Starkiller Base out so quickly after it was introduced. Unlike the DS which was established in the opening crawl of ANH, Starkiller Base didn't appear until like an hour into the movie and didn't even last to the end. I assumed that with it being as massive as it was that it would be the SW equivalent of Mount Doom and that it would be a threat until the end of Episode 9. Guess not.
Maybe that's part of the reason Starkiller base, despite all its power, just didn't come across as very threatening. ''What's that, oh it's another superweapon. Huh, it can blow up five planets we've never been to before, killing no characters of any importance.'' And with TFA having more humour aswell it sorta knocked the stakes down. When the characters don't seem particularly worried I guess I won't be either.
Compare this to Rogue One with a far less powerful superweapon.