I don't completely agree that Heisenberg first comes out in Walter when he asserts his will with Tuco. There's the scene where he shorts the BMW battery to get petty revenge on a douchebag that mildly inconvenienced him earlier, and of course the scene where he assaults the bully who was teasing Junior while buying jeans. It's akin to Batman Begins where Bruce first goes out in armor and harness but no cowl or cape. He slowly makes manifest in the real world the complete character in his mind. It's not a perfect comparison, but I see it as Walter allowing his true desire to come out more and more until it becomes his actual identity. The last remnant of Walter was let go when he finally admitted to Skyler that he did it all for himself. Mild-mannered Walter was doing it for the family so something would be left, but all along that was never true.
I think an interesting parallel can be seen between the character progression of Walter into Heisenberg and what we know of Saul Goodman to give us insight into Better Call Saul. (Spoilers I guess if you haven't watched it yet)
We start out knowing Walter White the high school chemistry teacher and watch him progress into Heisenberg, but there was a different character before that. There was Walter White the prestigious research chemist and co-founder of the innovative Grey Matter. The character progression of Walter the teacher into Heisenberg is an adulterated attempt to return to the version of Walter we the audience are only told about in retrospect; the person Walter White truly desires to be. We see in BCS that James McGill is, at this point in his life, a low-tier do-gooder. And we know from BB that Saul Goodman is a smarmy "criminal" lawyer. But in the first episode we the audience again are told in retrospect of the initial character; Slippin' Jimmy. Clearly from the way James McGill tells the story that he enjoyed being Slippin' Jimmy. He talks about how everybody wanted to shake his hand. He had money and a modicum of fame, he enjoyed what he did and he did it better than anyone. And just like Batman and Heisenberg, Saul Goodman is going to come out in James McGill because that is his true identity.