Oh, I agree to some extent. They don't need to deviate themselves from what makes Destiny, Destiny at its core. But introducing fundamental changes and new additions to what usually a sequel brings in, is the depth people were looking for.
Meaning new ways to play from a gameplay mechanic perspective (Third person, piloting ships, more melee executions, stealth combat, different ways to approach combat, etc).
And other basic things such as new sub classes, new enemies, new vehicles, actual open world exploration like Destiny 1 envisioned, revamped PVP with actual vehicles being a more dominant format in combat, own your own house somehwere in the Last City, customize your own ship, a new galaxy, etc.
Incremental changes that provide people with the intensity of a sequel so that they jump in to the next iteration.
Destiny 2 isn't living up to any of this.