Origins had a slot limit, it just had a wheel you could pick from, which I always found kind of annoying. Even on the PC, you only had like 12 slots. I really don't think the removal of 4 (which were primarily my crafting/pickpocketing slots) is going to damage the game. It's just one of those complaints that's basically "It's not like how it was in Origins!" that seem to permeate the forums. Just going to throw this out there: Origins combat was terrible. Agree. Disagree. Whatever. It's true.
Also, as far as multiplayer affecting single player, the concept of diminishing returns is one that exists within game development. At some point, writers/artists have reached a creative peak within one focus and then it starts to ebb. You can only get so many dishes clean with a sponge before having to run it under the tap again. Sure, they could have added more stuff to the game, but that stuff might not have been as good, or might not have had an impact, or might not have been written well. Instead, you wrap the project up and have people working on full additional content, or even the pre-production stages of DA4 or, god forbid, taking a vacation. So yes, multiplayer does take funding and resources, but it doesn't necessarily take them away from the single player experience in any meaningful way. People can tell me that it is so until they're blue in the face, but until they show me that multiplayer forced Casey Hudson and Mac Walters into a room to hammer together one of the (at the very VERY least) head scratching endings to a video game, I'm going to go ahead and reply by saying it's just your opinion, you have no basic in fact, and it's happening so get over it. Better yet, get some friends together and run some of the multiplayer. If it's anything like Mass Effect 3's, it'll be fun as hell.