$2,395 + ($215 * 10 years) = $4,545 / 10 years = $454.50/year, additional cost.
Now the skim. Lets say your MF is $1200/year/week = $300/day. If Marriott skims off 1-day/year that's a loss of $300/year.
Now you have $454.50 + $300 = $754.50 additional cost/year to use Marriott points each year for 6 days. Naturally, you can subtract the II fee's out that you would pay for the use of 7-days.
What's also missing from the equation is the cost to buy/rent additional points for that missing day that was skimmed. What would the cost be to buy an additional day at MOC or Ko'olina? I've read that the average price/point is $11.96. So, if someone needed 500 points, that would be $11.96 * 500 = $5,980 for 1-nite?? Am I missing something?
Not trying to argue or start an argument, just looking at the numbers and scratching my head in bewilderment.
Most people would adjust your top equation to $215 (or 175) less $89 (annual DC fee vs annual II fee). Still, there is a lot to make up for. Also, the skim for most resorts is 6-10%, so for most weeks it works out to be less than a day (so for your posted example, $120 would be a more likely amount instead of $300), but there are exceptions to that, too, where the skim is much worse (even more than $300 worse - that's back to dioxide's all skim isn't equal point).
The 3780 bonus points are worth something, certainly like a decent getaway on II. Most people would subtract that out of the cost if they can use it/rent it as m61376 pointed out.
The 11.96/pt is to purchase, and yes, 5980 would be crazy to pay for a night! But you can't even buy in 500pt packages (supposedly) so be ready to spring for at least 1000 pts....
However, the point rental price is substantially different. You can rent points for $0.50-0.60/pt, so a 500 point night would cost around $250 or so, and there are occasionally last minute point sales to be had as well. You'll notice most people on TUG advise to rent points if you need them rather than buy them since they are so expensive to buy but relatively cheap to rent.
Like DanCali said earlier, overall points in the system does not equal overall points awarded, and that's just gravy for Marriott.
Even though we can nitpick the numbers, your point stands: converting to DC points results in a small to moderate loss to weeks owners. However, despite that, there still is the example of the exchange I priced out; I can actually come out ahead using DC vs renting or II (due to the leftover points I can rent out). Does Marriott still come out ahead? Absolutely. They get the skim the second I convert, but I only can choose the options available to me if I don't choose to use my week: exchange with II, rent my week out & use the cash to book my week, or use the DC. For most weeks' owners, II gives the best values. Some weeks can rent for exorbitantly high rates, thus renting is almost always the best value. And in particular cases, the DC can work out well when DC points needed are less than rental rates.
The fee savings people talk about are by joining the DC but then using II - a lot! For the example I mentioned before (exchanging 5 lockoffs), here's how that would break down: annual II fee (89) + 10 exchange fees (10*124) + 5 lock-off fees (5*80) = $1729 in fees, all of which would be covered by the one time 2395 fee and an 215 annual DC fee, and that doesn't include any uptrade fees or the value of the 3780 pts. In two years you'd spend $2895 with the DC (joining fee + 2 annual fees), whereas if you did that many trades in II, you'd spend $3458. Obviously the money saved is drastically reduced for those with less holdings/less trades, but that is the math that enticed a lot of people.
We have people on the board who love the DC because they like the booking process (no waiting for II to come thru) & frequently book stays that aren't in the 7 day traditional block. Are they paying a good bit to do that? Yup, but it works for what they want.
Santa just finished eating cookies & drinking milk and the reindeer have had some carrot greens, so off to bed. Merry Christmas!