It sounds like people have a really warped sense of what makes up a Happy Ending. People are so quick to jump on the idea of everything being nothing but sunshine and flowers and everyone lives happily ever after. For one, I worry about the sort of people who believe that people being happy and alive is a bad thing. The idea that just because things turn out really well for all involved somehow makes such an ending invalid is flat out wrong - and that's something you just can't convince me otherwise. It might be a less interesting ending, but that doesn't make it invalid. But then most people are also mistaken when they assume that this is all a happy ending can be.
What's most important about what makes a happy ending is simply that it's an ending that you are happy with. The details of what makes up such an ending will vary greatly with different people. ( all the more reason why having a range of ending options is so important ) Sure some people will want unicorns and rainbows for everyone, but some people are happier with a noble sacrifice for their ending. Others want a grim but worthwhile hardship leading to a better world. Others want to see the world burn knowing that it was better then submitting to something they hated. While broad examples, the key is that whatever the actual end, the person playing it can walk away happy and satisfied with the resolution. Whatever the end is, the goal is for the ending to be something the player enjoys. This is hugely important, particularly for a game. Something which - annoyingly - so many people seem to forget. At its core the whole point of a game is to entertain the player. If the player walks away from a game and they're not happy then that product is a failure as a game. Full Stop.
Arguing about introspective purposes or artistic nuances of such an ending is meaningless in that regard. Certainly from a purely artisitc standpoint you can make a decidedly non-enoyable ending with the purpose to express whatever artistic measure you wish to convey. I don't argue that you can create such artwork very successfully. And no doubt there will be someone who will enjoy that. But for the average person that walks away feeling worse for it, whatever else it may be, it is no longer a game. Or at the very least, it's no longer a good game.
And yes, this does mean that on the opposite side of the spectrum you can have an ending filled with candy and Disney characters dancing all over the place and still have it be a terrible ending. Particularly if it comes off as undeserved or worthless.
There is a never-ending discussion of how to create an ending that players will be happy with. That is, in part, what game developers work at constantly. Like many people here I also enjoy the idea of an optimal ending where everyone you care about wins in some fashion being something you have to work hard for. Something to earn through whatever high challenge the game can provide. This is integral to the concept of risk/reward in gaming. To make such an optimal ending a reward for player who do put in the work and do make the effort to reach it.
There is absolutely nothing wrong whatsoever about an optimal ending being a reward for a thorough playthrough. If such a level of success is a reward for all the time spent grinding away at every nook and cranny of the game it is in its own way ENTIRELY deserved. Most people don't even finish the whole game, fewer still put in the effort to do absolutely everything they can. So they are completely justified in my opinion with a reward at the end for it. Mind you, my preference is more on worthy story elements and game challenges determining how optimal your ending becomes. Something which many of Bioware's games excel at. But then everyone will have a different level of what they would be willing to endure or deal with in order to feel they have earned a better ending.
I think an excellent example of this is the Genophage arc of the Mass Effect series. To get the absolute best possible ending you had to absolutely work your ass off to get it. Not only did it require completing a number of missions successfully, but it also required making the right choices, making sure the right people survive, and making the right things happen. Wrex, Mordin, Eve, all alive, all working together, and that's before you even reach Tuchanka. And if you skip out on the wrong side missions, all you efforts could be undone.
And after all that, Mordin still dies, sacrificing himself to save the Krogans.
That is a happy ending. Genophage cured, Mordin redeemed, Wrex and Eve leading the Krogans into a new age. This wasn't something simply handed to players, this was something you had to earn. There was real hardship and sacrifice required to get there, but the result was something truly wonderful.
The Geth-Quarian war was the same way, it's a huge challenge to get all the elements down just right if you want to save everyone. And even in the best case scenario you will still lose Legion.
People like to criticize the suicide mission in ME2, but I really liked the idea that it was possible to come out with everyone alive. I loved the idea that everyone else would constantly assuming that there was no way to come out of it alive, simply because no one ever has. Shepard, however, was determined to prove everyone wrong. It was a challenge to do so and required the right resources and the right decisions in order to make it out the other side. I think it's fair to argue that it should have been harder to accomplish a suicide mission without any casualties. But the notion it itself I found nothing wrong with.
ME3's endings by contrast were a disaster. It wasn't simply that there was no happy ending in any of them, it was that there was no way to walk away from any of the endings feeling any sense of satisfaction, much less enjoyment. No matter how hard you worked, or what decisions you made, what you were left with in the end was never something you could be happy with.
To bring it closer to home, DA:O's endings were very well done, with a wide range of options to give people an ending they would be happy with. For some it was marrying the king/queen and becoming royalty, while others were more then happy making the noble sacrifice knowing that there would be no one less old god to worry about in the future of Thedas. Others were more then happy to risk whatever the future may hold with the Old God baby knowing that their enemies were defeated and they remained alive to deal with the consequences should it come to that.
What's more, for truly optimal endings in DA:O you had to complete a large number of missions, and do so in the right way, so that the final world state could be tailors to something you truly can be happy with.
DA2's endings, however, were much more limited. No matter what your actions were, you remain the one blamed for igniting the Mage-Templar war. For some the way they were able to handle that still left them quite happy with the end of that story. While for others, being forced into that position and possibly feeling no sense of agency or resolution of those events could leave them very unhappy indeed.
Whatever ending the Inquisition might bring, I intend to put in all the work and effort required to reach an ending I'm happy with. Just make sure such an ending exists in the first place.