You thought you rambled; here’s a hodgepodge set of my thoughts.
I’ve sailed all three cruise lines you are considering, doing Princess three times in the middle. Most of my other sailing has been on Disney. I will be trying
Royal Caribbean out of Seattle in about a month - the first week in May (and only 5 nights).
We’ve never sailed with children who do clubs. Just teens and above, who spent most of their time with us or exploring the ship on their own (no daycare and homeschooled).
For a first visit to AK, I wouldn’t say there is not a specific set of ports that are a must-do. Most 7-night cruises are going to include Juneau, Skagway, and Ketchikan. And include a day viewing a glacier. If you don’t find AK spectacular enough to go back, ANY itinerary is fine.

. I have never repeated an itinerary. Nor ship.
The
DCL cruise aspect won’t differ that much from your previous cruise; smaller ship, more of the Fab 5 in seasonal / geographic garb wandering the ship on Glacier-viewing day. But similar food, entertainment, the Disney look / vibe.
We switched to Princess on the advice from a mother of many children (including 5 yo twins) - and a big Disney cruiser. She said her kids enjoyed the Princess kids’ club.
As far as kids’ clubs, you are typically only going to have two days when you will have a large amount of ship time - the first full day and the last or next-to last.
Budget is a big consideration for me (I’d rather have more vacations than more-expensive ones). As far as AK cruising goes, I want to be able to do big excursions, so I try to keep down the cruise cost and flights. (A balcony on Disney can be double (this is not hyperbole) what others cruise lines’ balconies sell for.)
So I pick Seattle over Vancouver (which usually means no Disney). I have done the flight to Seattle and taken Amtrak to Vancouver to save (that was a fun experience). Checking flights for a May cruise, Vancouver was in the $1200 range v. $600-700 for Seattle.
Likewise, hotels are cheaper in Seattle, with seemingly more options available. And comparably as nice ones, too.
Vancouver is a beautiful city; I would say it’s nicer, but one or two days pre-cruise in either city is not that different.
Most cruise lines offer many of the same excursions at similar prices; if there is something unique you really want to do, that could be a great decider.
My NCL cruise was very adult-oriented. I’ll take Disney entertainment over anybody else’s, based on quality and subject. The bars are more attended than Disney; the one in the Atrium, next to the area for trivia and music, was never empty. I have never noticed a crowd in the Dream’s Atrium bar, nor the Promenade Lounge. [I was on a cruise with no one under 12 yo, due to vaccination requirements.] They often have a free drinks offer.
NCL’s Encore (it has a sister, the Bliss) won me over for actual ship. They were purpose-built for cruising AK, with a large, glass-walled Observation Lounge (the front third or fourth of Deck 15) and a large walking / sitting space on Deck 8.
Princess has been a leader in AK. They bring on a ranger to do talks and presentations. They are allowed to sail in Glacier Bay, which is a limited group of cruise lines (Disney does not; NCL does). The rooms run on the smaller side in some categories, although the mini-suite does offer a large sitting/sofa area, two TVs, and a real bathtub. And would probably be a lot less expensive than a regular balcony on DCL. We enjoyed eating in the buffet on days we went on excursions; more variety and less formal than MDRs.
Most likely, in 2023 (only change was for 2021), you will stop in Victoria, BC, for a distant port stop requirement when sailing RT from Seattle. This is often at night, with little to do.
Disney
+ smaller ship (Wonder)
+ kid-friendly entertainment (great for all ages who enjoy Disney)
+ Vancouver (easy access to port from most hotels)
-Vancouver (only) w/increased airfare and lodging
-Price
NCL
+Bliss or Encore ship, designed for AK cruising. Larger, newer ships
+ Sails from Seattle
+ Lower fares
+ Free drinks and Specialty Dining offers
-Adult-oriented entertainment
Princess
+Ships built for AK
+Lower fares
+Solid reputation
-Less kid-friendly entertainment
Other than transportation and cruise fare cost, I would ask how much evening entertainment matters to your family. And how much you enjoy Disney entertainment.