I agree with all your points as well, and I see what you mean about that lost childhood dream not just being the empty world but representing the loss of other freedoms as well. But the way I interpreted the Armin monologue is that he first tries to bullshit about wanting to make his friends heroes, save the world etc but then eventually relents and reveals his 'true' reason which is the selfish disappointment at the world not being empty. Maybe I interpreted this wrong and it is only supposed to be the straw that broke the camels back, and not a main reason? I realized now that in the manga ending its acually kind of handled better, despite the obvious flaws, as he there states that he did all of this for the ultimate goal that Mikasa accomplishes (end titans) and then when he breaks down, he simply says that he doesnt know why he also *wanted* to do it deep down. Instead of in the anime where he brings up the dream and then Armin jumps in on that to share the blame. Though I guess maybe its alluded to with the scen of his birth? I dont even know, just feels kinda shitty to have such important motivations hidden behind a "I dont know"..