Honestly sounds like you want a destiny 1 remaster that's updated with d2s QOL changes. Actually... That might be a good idea. D1 remaster/ remake where they give it qol updates and just start making new content for it. Give it new expansions. Write a completely new story like d2 never happened. Would probably be better than what we have now. Then most of what you want is just there.
Or take what D1 currently is, add the QoL of D2, and combine the two narratives into one massive game.
Rework old D1 and D2 campaigns to be brought up on par with the likes of Witch Queen (Not narrative structure, but mission structure.) this will and would be easier with Campaigns like those in D1 and very narrative oriented campaigns like Red War. Forsaken, Shadowkeep, and smaller campaigns would be harder to redesign to fit the structure Which Queen had set.
Reintroduce Strike Specific Loot and make them essentially exotic Legendaries. And with the drop chance of a Raid Exotic too, though increase the chance as the difficulty increases.
With Armor 3.0, we can now have specific cosmetics tied to specific armor pieces. So for armor, we could keep the transmog system, but specific gear also have Cosmetic Tokens (like those from the Age of Triumph Raids) that can only be applied to armor that comes from that specific activity. So you have to use that specific piece, and you don’t just get the cosmetic to apply to any gear. This adds another level of novelty to gear and gives it value besides set bonuses.
The Portal is cool, but I think it wildly misses the mark, and just confuses people who were use to the old system. On top of that, I think it’s just too much and takes away from the Directory, which was super cool. Having customization is a good thing, but making it so that it takes away from curated content that is designed to be difficult and hard is an inherent negative. Maybe it’s just me, but GMs don’t feel like GMs anymore.