For my family, capturing photos with the characters in their various outfits and the formal and semi-formal nights photo opportunities were more important than the traditional backdrop photos or pictures in places like Magic Kingdom. We also really appreciated the more personalized interactions with the characters on the cruise, and how the photographers took extra time to help pose us, compared to the quicker pace in the parks.
I think characters are the one category where you get more out of the ship package than the parks package. You're right that they have a variety of outfits and the interactions are great. But, you can also ask them to use your phone to take character photos and they will happily oblige you.
My girls are all-in on magic shots and ride photos (they have us decide how we're going to pose in the leadup to various coasters) and those can't just be snapped with one's personal device. While there are scheduled times for magic shots on board, there's nowhere near the variety you can get in the parks, where you can essentially ask every PP if they have a magic shot a they'll be able to come up with something. And, photopass in general are only available at specific times with
DCL. So, if you have downtime in the middle of the day, you can't just stop and grab a quick family photo, like you can in the parks.
Also, because OP mentioned
MNSSHP, I would also suggest the parks package is especially valuable because night shots in general are just so much better lit with the PP cameras, especially if you're meeting some of the rare characters in the dark. And, of course, the party-specific magic shots, if that's your thing.
When I look back, my cruise photos are arguably nicer, since we're not sweaty messes who've walked miles each day. But, the favorites inevitably come from WDW, not DCL.