Season 6 was quite good, it was the closest to S1, I'd say. However, 6B was indeed less good than 6A. I think after 614 the story was a bit lost, some things were quite rushed and, yes, they wasted time this season with stuff like Aladdn, Jasmine and the Oracle (who turned out to mean nothing at all). The red bird thing, Emma's visions, the origins of the Black Fairy, the Savior Mithology were all poorly developed, but overall the season was planned in a much better way than S5 and even, I'd say, 3B (which I always considered worse than S2, despite nearly everyone loving 3B).
People complain about 4A, but I find it very good job. It is solid, has no plot holes and the writing is well-done.
As to the Untold Stories, I think they complicate themselves with metalinguistic things, like characters (who are supposed to be people) discussing stuff like "happy endings, untold stories, unfinished business" etc. What makes a story untold? In our perspective as viewers, unfinished business in S5 could make one expect to see Will and Ana, Mal and Lily etc. Untold stories could mean the same, but turns out it went nowhere. In fact, a season promoted as the season of untold stories had literally ONE scene in LoUS, and a very short one with only Mr. Gold.
I do, however, like what they did with that premise with Edmond, Ella's family and Jekyll. I loved Jekyll and Hyde's arc, and it was the kind of thing that, even if too short, is satisfying, much more than a story that goes on for a whole midseason and ends with no logic (like Merlin, Nimue, Hook, Camelot , Merida etc. in 5A) or a story that should be longer and is squeezed in 1 flashback (like Fiona's).
Overall, I'd say that Aladdin and Jasmine, though amazingly portrayed by Deniz and Karen, served to no purpose and the season would have been way better without them. The savior thing perhaps would work even better if Emma was the one and only savior, with no need to add a former savior whose mithology ended up pointless.