I disagree entirely. Not only is getting Sanji back and the Poneglyph MAJOR developments, but they also got a new crewmember in Jinbei. Also, this changes the dynamic of Luffy's feud with Big Mom, as now she'll likely be pursuing him as an Emperor would do, a conflict the crew has never faced before.
I said the overall story. Saying that getting Sanji back is a major development is a farce. Sanji has been a Strawhat for over 700 consecutive characters. The Strawhats were already separated halfway through the Dressrosa arc, they are still separated and being in separate groups is nothing new. Sanji originally didn't say either he left the crew, just that he was gone for a while. Only during the arc itself he officially left, but that was quickly resolved afterwards. So nothing really changed as the problems only occurred during the arc itself. Sanji permanently leaving, now that would have been a major development and be realistic here, no one doubted he would remain a strawhat.
In fact seen from a global perspective it can be said that the whole Sanji thing has halted the story as everything is more or less the same before and after the arc when it concerns Sanji. Yes for Sanji as an individual character this arc was very important, but for the story not so much. At least as it stands now as it's always possible Oda gives it a twist in the future, but currently: no.
And yes they have now two new Poneglyph which will be an important key in the long run, however tell me how much time was spent on them? How much panels or attention did they receive? Not much, huh. If it was just the Poneglyph, this arc should have been wrapped up a long time ago. So again this is not really that major.
BM being mad at the Strawhats? She was already mad, she was going to crush/hunt them either way, something she specifically said to Luffy on FI. Yes she's now way more pissed, but again in the end that doesn't matter that much. You didn't need an entire arc for that as she was obliged to pursue them sooner or later either way.
Jinbei? Yes him becoming an official member is quite a big deal, but truthfully Jinbei was already in the zone of being part of Luffy's forces to the point many people were already considering him to be a member. There is definitely a difference between Jinbei being an actual crew member traveling with them and him just being an ally, but again compared to the length of this arc Jinbei's joining is only a subplot that already had been brewing all the way back since Marineford arc.
What I'm talking about there is the arc as a whole, not some individual, isolated events, and yes this arc still very well misses a result. Two of the things you said are really not correct as BM's animosity and Sanji's situation are more or less the same before and after the arc and the poneglyph and Jinbei are really not in proportion to the entire arc. The fact that the Strawhats had everything you just listed already before the climax of this arc, pretty much proves my point. If BM destroys the island and kills half of her crew, well that definitely will have some nasty consequences for her in the near future and she became like that due to everything that occurred during the arc.
