That's 2 games you cherry picked...and considering they overhauled PVP, added 4 new planets, with all new story, like every sequel. How is Gears 2 a sequel and Destiny 2 not?
Faction wars is new
Adventures - New
Lost Sectors - New
It's a sequel by the very definition.
As I said, it's the example in the OP.
The PvP stuff, now that's a sequel-worthy change. Fair enough. I haven't dabbled in that, so it didn't come to mind.