To be fair, DAK is more than rides - there are a lot of good shows and diversions throughout the park that help fill out a day. Also, rides like Kali, Kilimanjaro, Everest and Dinosaur are all high capacity as well. To the point however, yes, I do think most of the extra guests going to DAK would've gone to Epcot or DHS anyway. High capacity or not though, no jump in wait times for other rides is definitely troubling.
However, where Universal and Disney run into an issue is that there is only so much vacation time. Disney waited FAR too long to react to Potter and now Disney will never be able to recover the guest days that they have lost due to complacency. So I feel like Disney has put them in a position where they can only take guests from themselves now... that's not terrible since with the yearly numbers they pull, but the issue is they need to be pulling people away from MK, not DHS or Epcot. MK will always be one of the busiest parks in the world, but they need DHS, Epcot and DAK to bite into MK's numbers by a few million if they are going to stay stagnant in attendance.
Universal will soon stop growing at such a rapid rate given that both Orlando parks are around 10M (or more depending on real numbers). It will actually be interesting when the south park gets underway and opens... how much will that affect USF and IOAs numbers? When DAK opened in 1998 for example, Epcot's attendance took a nose dive. Disney has been stealing attendance from itself virtually ever since then - remember, SeaWorld used to have a much higher percentage of the market share (and in SW's decline, Uni has mostly grabbed those numbers).
So yeah, spending this type of money and not seeing much except a change in crowd patterns isn't exactly what you want, but by this point, they should bee used to it, and honestly it's what they deserve - especially after ignoring Potter for years out of a sheer "they'll always be #2" attitude.