We paid $300/night after fees for Dolphin for Princess with the AP rate last year, and I got the first couple nights of January before Marathon Weekend 2023 for like $220, which was cheaper than Pop rack rates! (Maybe not cheaper than Pop with the AP discount but they weren't available yet when I booked so it's not any of my business
). If you are just looking at rates occasionally, you are probably never seeing the low prices. I would say 99% of the time S/D are pretty expensive and then a few random days the rates will magically drop so it definitely takes some diligent checking to get good deals, all thanks to Marriott's dynamic pricing. I do not ever need parking though, so that helps keep it "cheaper."
S/D are great when you want the deluxe benefits for way less than deluxe prices, assuming you get a good AP rate. It probably isn't a good deal if you don't have an AP. I would say it's comparable to renting DVC but without any of the risk or needing to book at 11 months. But it does sound seem like their rates have gone up a lot for 2024/2025, they are realizing how good of a value it is...and that us runDisney folks are locked into our dates, they can take advantage of that!