Destiny 1 had a cool idea, but you could tell it got chopped up to be resold as DLC later. It was certainly more “finished” as a concept than D2, but after a few DLCs the game was kinda soured. It was basically just quasi-MMO Halo Reach still at that point.
The Dreadnaught, which was my favorite area in D1, was originally the vanilla endgame area. It was planned to be in the game from the beginning. Joe Staten literally had everything all laid out, and Jason Jones banned him from working on it and stole all his ideas, then hacked them all to pieces.