I agreed with everything you said until you argued that putting more money in the developer's hands makes the game better.
In a perfect world, yes, that's what would happen. However, Destiny made back their development costs in the first week of sales and its taken a whole a year to see substantial improvement.
Don't get me wrong, I see the remaking of the first year with quests and a new ghost voice as an apology and attempt to improve (therefore deserving of a second chance), but I really doubt that they're going to use this dlc money to make the game better.
I guess j should have stated that point better. You're right, it is not a guarantee that it will. The only effect, save for my wallet getting a little thinner, that buying this DLC has is giving this game more of a chance to get better. Nothing for sure, but it doesn't actually hurt the developer earning more money. Could they sit on it? Sure, but if I want the items anyway, and they seem valuable enough to me, then it's a win-win.