Killing Disney? No. Genius? Yes.
Regardless of whether you love, hate, or are indifferent to the plans themselves I think the key here is something that OP mentioned actually...ADR are hard to get and almost all table service restaurants are booked to capacity. Disney is at the point where they need to open MORE restaurants to accommodate their guests.
I don't work in the restaurant industry but I would guess than full restaurant seatings every day is GREAT for business. IF there is/has been a drop in the quality of the food, the service, etc then it clearly isn't enough to drive away the business at this point because table service restaurants with walk up availability are few and far between at Disney World.
Prices are high, in my opinion, but not higher than I would expect to pay in a theme park and every meal I have had there has been better than what I have had at Chilis, Applebees, and other similar chains. That, of course, is sort of beside the point though. The prices are what they are and people pay them. From a business perspective, why WOULDN'T you charge what people are willing to pay so long as you have your restaurants booked to capacity every day? At the end of the day...Disney is a business and for all the things we want (new rides, park experiences, rehabs, etc) they have to pay for these things some how while still making a profit.
Will some people (and have some people) boycott the table service restaurants because of the prices, quality of food, and quality of service? Sure...but there are hundreds of people waiting behind them to take their ADRs. So while Disney in those situations might be losing customers they are not losing business because restuarants are still booked up.
If Disney can open more restaurants to accommodate all the guests looking for ADRs without opening TOO many (where they can't FILL those restaurants) then they will continue to make more and more money off the dining plans. Whether guests pay OOP or pay with the dining plan...it's still money in their pockets. And with the system they have they are booking most restaurants to capacity every day. It may be frustrating as a guest to have to plan so far in advance, to not be able to walk up to a sit down restaurant without a reservation and eat a meal, etc but from a business perspective on Disney's end...it's not a frustration that has cost them any business. And I personally think that if they can open several new restaurants to accommodate their guests in the parks (and it sounds like from rumors that they are planning to) it won't cost them any business in the future either.
And for the QS dining plan...I also think this is genius for Disney. Those become guaranteed meals that guests eat on property instead of them bringing in extra food or eating offsite. There are more than enough places to accommodate all the guests who want to eat QS meals and I don't think offering a QS dining plan really COSTS them anything and the profit comes from that guaranteed income on those sales.
Also an added bonus with the dining plans in general is that people don't have to leave the property and because they have already paid for the dining plans they spend more time in the parks...often spending more money. So you've got the onsite MEALS these guests have and are spending money on PLUS the added time for them to stay in the parks and buy more things. I'm sure Disney has people that analyze all of these things and know exactly how the dining plans impact their bottom line.
My guess is that dining plans will be around for a VERY long time, as will free dining promotions. They have definitely changed the way people vacation at Disney, and I would guess the impact was more than even Disney realized when they first rolled out the original
Disney Dining plan. But it's all been good for business...of that I am pretty sure.