Disagree.
DVC saves the consumer money in the mid- to long- term. (As you say, at best in 8-10 years if compared to staying deluxe and buy direct, or if you normally stay moderate and buy resale. Longer if you normally stay moderate and buy direct.)
What Disney likes, as any business does, is that they (1) get the money from your stay up front and (2) they lock you in to spend your future money at Disney.
As for #1, most big businesses only worry about the next quarter/year. DVC gets people to pony up 10 years worth of stays up front. Then they collect enough money to cover the resort expenses (Maintenance Fees) each year. In this way, DVC only works as long as they continue to sell DVC units. There needs to always be a new DVC resorts. However, the profit for Disney is in that up front sale.
As for #2, the hotel stay is only a portion of your vacation dollar. There's park tickets, food, merchandise. All things the DVC customer will continue to buy ad infinitum. So this is a win for Disney as well.
However, the consumer clearly benefits from this in the long run. Ask anyone that bought into DVC 10+ years ago and still owns it if they are saving money. There's not one of them that won't tell you yes. (Well, you are correct in that SOME of them are probably now staying in 1 bedrooms instead of hotel rooms, and so therefore are spending as much as they used to for nicer accommodations.)