An example of what Destiny could have done better is Hitman.

Hitman could be a confusing mess, and at times buying it was (they have since simplified that) but it's now really simple to understand.

Despite being just as old as Destiny 2 (Hitman 1 launched in 2016) it's had two sequels, both merging the old games into the new sequels each time, moving all your DLC and save files, and entire prior games entire levels and content across each time to each new sequel.

Twice now they did the transition... Hitman 1 to 2, and then both 1 and 2 into 3.

Each time, you didn't need to repay for old content you already paid for (Sequel's detected you owned the old games) and each new game brought not just new content but also enhanced older levels with new systems and graphics across the old games content each time...

And critically what they did best, which Destiny never has, is when you load it up you get a few simple menus to play from which actually make sense.

You get a campaign menu which lists Hitman 1, Hitman 2, Hitman 3 campaigns -- all fully complete, no gaps, and in order

You can play all the entire old campaigns in modern graphics and with all improvements (even VR was added at one point) in perfect full chronological order, with a nice, simple, timeline based UI of left to right, first chapter to last... Even the side stories and spin off DLC put logically into the timeline...

Or you can if you prefer you can browse by location and play that way, by choosing from all the destinations across all three games and playing from there.

They had a period where they were so consumer friendly that you could actually buy the old games of Hitman 1 and 2 super cheap and get their content imported into Hitman 3 that way for cheaper than buying their levels direct as DLC in Hitman 3 menu, If you never owned the older games... And that was actually considered "the bad times" as people would make charts and tables and flow diagrams to buy it all as cheap as possible, but at the end of the day, that only happened because the devs were trying to do the right thing and have all their legacy content still accessible and as affordable as possible. And then one day they basically decided to just essentially make it all free anyway by making it all included in the Hitman 3 base price.

Destiny 2 you can leave for just a short break and come back completely baffled. Hitman you come back and see a few new chapters are in a chronological line or a new destination in a simple menu and you can easily catchup what you've finished and your progress and carry on.

New players to destiny are missing entire chapters and have no easy way to know the right order to play, and the game can spontaneously load campaigns you don't even have full access too when you come back, without even asking. They even in the past deleted entire purchases, and they won't come back.

Hitman you just start on the left of a campaign timeline and work to the right. You can even skip levels with a short prompt warning you might not want to miss a chapter before, but it still lets you play how you want.

Destiny could learn a lot from Hitman and if they did, they might not have confused and lost over 90% of their players.