As someone who loved Heavensward to then be completely disappointed with the Stormblood story, to the point of taking a break from the game, I would say it gets a lot better with the Shadowbringers prepatch and its main story.
Funny how I disliked the story of Stormblood but came to absolutely love its content instead, like Eureka, Deep Dungeon, glamour, and certain dungeons/Extremes/Omega.

I'm currently having the same issue with Endwalker's story, of being really meh but hoping for its content to deliver in some areas at least, like we are finally getting a new Deep Dungeon soon! And also the Alliance raid so far has been phenomenal, Extremes been enjoyable, while Island Sanctuary and Criterion have been complete duds.

Stormblood story really had some glaring issues with pacing and some of its story just being a mindboggling mess of an affair. I sometimes wonder why they chose to change Yda into Lyse, and propel her infront of someone else, like say, Raubahn? Raubahn seemed like the perfect character to venture into all of Stormblood to reclaim it and come to terms with his own views and Ilberd's points of views and his clear anguish leading to his down maniac actions and death. Could have been an amazing retread of Raubahn's past, with some better threads between him and the villains, past and present, it could have been a very interesting path of reclamation and reflection.
Not to mention that Gosetsu and Tsuyu could have been so much more, within the main story arc as well.