They have two teams, the core team that is probably working on Destiny 3 (or another game?) already and the live team that has been working on the DLCs since the game launched. I don't have any hard numbers but I'd assume the main team is like 200+ and the live team is like 20-40 people, so of course the content is going to be small and reuse a lot of assets like MMOs.
I guess the only real question is how fast will you exhaust the DLC 1 content, like ... 3 days? 7 days? 10 days, max? Having a new wing for a new raid in the same textured area sounds really boring and lame, and I don't even understand how it would fit in story wise. "Ho ho ho, you beat my robot slave that was pretending to be me, I have now prepared a seperate gladiator arena for you to fight in that I didn't have ready 3 months ago! Yeah, this makes no sense to me either, just go kill shit and get some loot ok."
Woulda been awesome to reuse VoG and put it into the Infinite Forest and fight Atheon v3.0 but I guess that just makes too much sense in a DLC centered around the vex. Wait, lemme guess, the Cabal emperor has captured some vex and brought them on his ship to fight you, because THAT makes a lot of sense.