It wasn’t about self-sacrifice, though. It was about genocide of friend (EDI and the geth) and foe (the Reapers) alike. That’s considerably different. It is even worse when a major theme of both ME2 and ME3 is the self-determination of EDI and the geth. It’s different if Shepard, or by extension humanity is sacrificing itself for everyone else – instead, the Destroy ending comes off as rather selfish to me.
I can understand that part, and that’s fine – I don’t have a problem with reflection, but I think that could have been done in a better way with a confrontation with an already-established antagonist (Harbinger) instead of a bunch of babble from a deus ex machina and then a literal “ignore anything that’s happened up till now, just pick the ending you want.” I also don’t think the confrontation with TIM is close to the same as with Saren – you literally can’t do a damn thing against TIM, whereas you can literally get Saren to kill himself. If it had the same overtones it surely doesn’t have the same kind of agency.
There is a difference between “happiness and sunshine” and “triumphant.” In ME1, along the way, you lost either Kaidan or Ashley, you might have killed Wrex, you might have had to listen to the Salarian commandos on Virmire fighting an unwinnable battle and dying while you desperately tried to take down Saren. You had to listen to Vigil telling you how he had been waiting for 50,000 years in the hopes that one day, he would be able to give hope to a new crop of sentient life after his contemporaries had all died to a one (well, almost, evidently). You might have lost the Council. Yes, Shepard emerges from the wreckage at the end and the galaxy is saved, but there is a cost that is paid for it. But it is really up to you and your choices how celebratory it really is.
In ME2, almost every character’s loyalty mission deals with a bittersweet part of their past. Miranda loses the only friend she ever really had. Jack finds out she was probably the luckiest of the children interned at Pragia. Mordin has to face a friend who can’t live with what they did. Jacob finds out his father is essentially a serial rapist and madman. Thane has to deal with his son following his same dark path. Even Kasumi and Zaeed have to deal with some pretty tough choices. Only Grunt really never has to confront his past…because he barely has one (and that is his burden). The lesson of every since loyalty mission, though, if you’re successful anyway, is that dealing with this kind of emotional issue makes you stronger – especially when you have friends (like Shepard) to depend on. The whole idea of the game is that Shepard is someone who can make great people even better. And all that stuff you did throughout the game gives you a better chance of getting through the end of the game triumphantly.
In ME3, the problem is that the themes of the rest of the game, which are similar (the krogan patching up things with the turians, the quarians with the geth, Shepard’s horror at what Cerberus is sacrificing for power) are completely contradictory to the themes of the three endings. It’s hard to feel triumphant about any of them, because in one you are literally killing the people who are evidence that the deus ex machina is wrong about organics and synthetics not getting along, one you are stomping on the whole idea of free will, and the other you are destroying the diversity that is supposedly what makes this whole cycle the strongest (also, it doesn’t make any goddamn sense, but that’s beside the point). That’s why I don’t feel good about any of them and they feel out of place with the previous three games (including ME3 up until that point).