What I'm saying is that it would not change overall Alliance policy, given how this can be pinned exclusively on Nathanos and Sylvanas unlike most everything the Alliance overlook, and its relatively narrow scope. In terms of Jaina's reaction, I'll freely admit that my position is purely speculation based on what we see of her before, since we don't know what would have happened, as it didn't actually happen. That having been said, I think given that her ultimate conclusion was that most in the Horde have at least the capacity to be fundamentally decent and lack responsibility and in turn, that Garrosh/Sylvanas were the bad eggs, and that the destruction of her city, the attacks on her people, etc. etc. by the Horde at large wouldn't change it, a crime upon her family inflicted by Sylvanas in particular would be unlikely to shake it.
If I were to steelman this entire scenario, I'd go with the fact that the flimsiness of the plan was intentional, as was its publicity. I.e, that Sylvanas publicly raised Derek to make the rest of the Horde culpable in it by being aware and not doing anything, and didn't care whether he killed Jaina or not because the real aim would be to piss Jaina off into throwing a compromise off the table. I don't actually buy this though, because the Horde is never privy to Jaina's character turn and still assumes she's out for blood, as evidenced by Rexxar or Talanji's position for instance, and that Jaina might waver would be needed for this to take place.
It's no secret that I loathe Baine as a character and what his actions actually entail with the vast gulf in how they're presented to us as some epitome of virtue. He's basically everything that's wrong with the Horde in narrative form. That being said, when I give Baine shit, it's when he does or doesn't do something - see his reaction to Taurajo, his actions with the Quillboar, betraying the Horde at Theramore, betraying the Horde with Derek, etc. You'll notice I haven't given Baine shit for say, trying to kill the void creatures in the tauren heritage scenario, recruiting the Highmountain, fighting the Grimtotem dude at the end of Mulgore, and the like. But those moments are few, far between and lack much to actually discuss in them as compared to the magnitude of his fuck-ups which are always a big story focus and always treated by the narrative in a fashion anemic that's incoherent and ridiculous in the broader scheme of things as well as contextually.This is a point in any single-minded dislike or outright hatred where you can't permit a character to be seen in any form of positive light. You'll over-emphasize them when they're at the worst, and recontextualize them into sucking when they're arguably at their best. The inverse is often true for characters people like - they can do not wrong, and when and if they do wrong it's often cause to justify them with obtuse metaphors or ecstatic rationalizations. Baine is flawed without a doubt, and he's done some truly dumb things as a leader - but even a stopped clock is right twice a day, the saying goes. An utter refusal to give Baine *any* possibility of doing the right thing is far from objective.
Treating them as separate events is honestly the most charitable interpretation that they can be given, because in that context at least you can occasionally plead a lack of awareness on his part or an inability to intervene. When he does actually intervene however, it's about an offense magnitudes more minor than the ones he ignored, that's where the issue is, along with what he chooses to stand up for. Let's recall what he first committed treason for after all, namely a conventional attack on a city with a heavy military presence that was an aggressor to his people, that being Theramore. Even the idea that it'd be attacked was enough for Baine to tip Jaina off. Yet he does not react when Teldrassil is burned, nor to the harm inflicted upon his people by the Warchief, much bigger things, nor to the routine stuff we mentioned before. The only differentiating line that remains is that he moved when his friends were hurt, in this case Jaina, but not elsewhere. Is that the intended reading? Of course, not but it is what we have. Baine standing put for all the things we've gabbed on about endlessly, but acting for Derek does not make him look good, it makes him appear worse and to care less about the Horde, the tauren or a general loss of life than he does about his own personal relationships.Everyone has their breaking point. You are treating each incident as an isolated and completely discrete occurrence, judging them solely on their merit in a vacuum and so insinuating there's no causal link between one occurrence and the next. "Because Baine didn't react to this, or this, then obviously this last thing is too minor to matter." Baine simply reached the limit of what he could allow, after a long time suffering Sylvanas' misdeeds in relative silence. Baine's made little bones of his opposition to Sylvanas and her methods throughout BfA, so we already know he's very critical of her. He doesn't act in light of Teldrassil, doesn't act in light of Lordaeron, bides his time in Zuldazar, but when push finally comes to shove and something comes along where he can act then he does so. That's a good thing, and one totally in keeping with his character. As for his role within the Horde and the very idea of his changing hearts and minds, the very narrative is against you there - with Lor'themar calling him "the Heart of the Horde" and major Horde leaders from Rokhan to Thrall to Lor'themar to Thalyssra falling in with the rebel sentiment and acting either to aid Saurfang in rescuing Baine directly or afterward, sensing that the time to oppose Sylvanas is nigh. Those at the leader summit summit against Sylvanas was circumspect and unsure of it, save for perhaps Mayla and Rexxar; but Baine's action galvanizes them and does much to lead to the later movement against Sylvanas when Saurfang returns to the Horde proper.
As for him rallying the leadership against Sylvanas, I'll give you that he becomes a martyr that drives the rest of these pansies to oppose her, but he also serves to further galvanize the Horde against them in terms of a mass movement. The killing of Horde troops in saving Baine alongside the Alliance and the public spectacle done of his sentencing which was deliberately engineered by Sylvanas to send a mass message both about his conduct and the cost of suffering is what ended up with the rebels being a minority instead of a majority when it came time to engage her and punted the ball over to Saurfang resolving the situation with Mak'gora. Both the publicity of Baine's sentencing and the break-in were ultimately harmful to the rebellion.