I think every time someone utters the words "dumbing down", they lose a finger. No better way to punish idiocy.
In what way does adding multiplayer make the game worse?
The overwhelming majority of AAA games utilize DRM and have been for some time now. While this is a bonus for CDPR as far as their customers are concerned, it's not a good idea for long term business.
No game has ever had free DLC before, ever.
Literally the only thing on your list unique to CDPR is the bit about DRM.
I kinda dislike the term "dumbing down" but it is the quickest way to describe that issue. You can't deny that a lot of games nowadays have they interesting features stripped or gutted in favor of more "streamlined" gameplay. It is good in some cases, but more often it hurts the game.
By taking away resources from the main game. Different people work on the MP, but all those money spent on it could be spent on improving the single player campaign in some way (be it extra content or fixes for the current buggy one). Again, the added MP can very well prolong the interest in the game as we could see in ME3 where it was done very well, but often almost nobody even plays the MP after realizing it sucks, since it was not needed and not wanted and it is in the game for one reason only - microtransactions.
Well, CD Projekt and its distribution service GoG are going pretty strong at the moment with no DRM, continuously expanding GoG's portfolio. It is in no small part thanks to the fact they are one of the very few to follow this path. If nobody put DRM in their games, they wouldn't get all that extra love and in turn, money.
Except the Witcher series
I don't know if there have been other games as well with free DLCs, there most likely were, I just don't know about them. But both previous Witcher games have received tremendous post-launch service. Enhanced editions upgrades, as well as DLCs were completely free and they improved the game significantly. The Enhanced Edition for Witcher 2 for example added not only extra bug fixes, but also extra quests, cinematics, narration between chapters and new intro and outro CG movie, among other things. The first Witcher 3 free DLCs are already scheduled.
Also as a bonus, CD Projekt doesn't follow the conversion rate of 1 USD = 1 EUR. When they did it in the case of Witcher 2, they added the real difference (which I believed was something around 15 USD) back to their customers' GoG accounts. DAI went (and still goes if not on sale) for 60 € on Origin in my country. Witcher 3 base price is 40 €, 36 € if pre-ordered, 34 € if one owns either the 1st or 2nd game and 32 € if one owns them both. On top of that you'll get NWN: Diamond Edition for free, comics, soundtrack, artbook and all that shizzle. What could I get for standard 60 € DAI pre-order? Few weapons, armors and one mount. If I wanted the soundtrack and more ingame bonuses, the game went for 70 €. Is the Witcher 3 going to be half the game DAI is since it costs half the money? Not really, it just shows they are not greedy bastards and actually treat their customers as they should be treated.