Yes, but the break even point for a DVC membership is not 50 years, or even 25 years. Depending on the contract, it’s in the teens or lower. This can obviously scale up or down depending on the “membership extras” you participate in, such as AP. But just strictly on the savings from rooms, the break even point isn’t that long.
Take Riviera, for example. The buy in cost for a 200 point contract would be $40,200. How long would it take to make up that cost with what you are saving in rooms? Well, in 2021 the MFs are $8.38/pt. So let’s say your family likes to go to Disney for the time around Christmas. A preferred view studio for a week at that time of year in 2021 is $7961 if you booked through Disney. The cost for that week via DVC’s $8.38/pt is $1,215. That’s a difference of $6,746. Divide the $40,200 buy in by $6,746 and it comes to 6 years. Granted, there are a lot of variables at play in this scenario that will affect the break even point: time of year when visiting, size of contract, room type, Disney discounts off of rack rate, MFs increasing each year, etc. And there are also other factors that can advance how quickly break even occurs such as AP discounts and renting out non used points. The point is that typically by year 12 your DVC membership has at least broken even. Fast forward years down the road and the amount being saved by owning DVC (assuming you would have stayed in a deluxe room every year) skyrockets.
I agree that it’s almost impossible to see 25 or 50 years down the road. However, most people have a pretty grasp if they will be able to utilize DVC for the next 10-15 years. That’s all it takes to at least break even. And that's all just the dollars and cents of it...none of that takes into consideration the joy experienced and memories made. As I said in an earlier comment, it's impossible to completely quantify a DVC membership.