The true narrative depth of Ultra Instinct mastery

Ultra instinct came out of nowhere especially since in all of Goku's battles the ability to dodge and attack faster than your opponents can predict/follow was simply an advantage of being so much stronger than them, no matter how many they were.

But from the narrative point of view, Ultra instinct mastery is just a continuation of Toriyama's idea that Goku needs to master techniques too and not just power-ups to prove how much stronger he's gotten.Goku learns one technique from each of his masters: 

1. Kamehameha from Master roshi, 
2. martial arts principles from korin, 
3. energy control from Kami, 
4. the Kaioken and spirit bomb from King Kai, and 
5. the instant transmission from Pybara of Planet Yardrat...

then suddenly Goku's no longer learning techniques, but just how to break his own limits and master new transformations. Goku's masters had been giving Goku strength training in various forms, but not with the intent that he'd be a meat bag that packed a punch, but a fighting wiz with a great command of their techniques. 

After going super saiyan, Goku figures out his great potential for more strength and trains harder to master all the super saiyan transformations he's capable of, even after dying in the Cell games.

Then, after meeting Whis, Goku masters heightening his energy internally without letting a drop out—unintentionally allowing him to ascend a level above super saiyan god.

Goku had been transforming over and over he had neglected the techniques, until he's faced with power he couldn't match; and after remembering the point of training with Whis in the first place, i.e., to master moving completely on instinct, is he able to grasp the incredible power of the gods' elite technique: ultra instinct.

Powering up isn't the point of Goku learning from his masters, it's the bonus he gets and Dragon Ball Super is the story of how Goku manages to let go of the lessons drawn from his battle experience (his super extreme battles against Freeza, Cell and Buu in all his iterations) and trust that mastering a difficult technique will close the gap.

Goku's battle against Jiren is akin to his first real fight against Vegeta where his strength is not the deciding factor, but his trust in his training, his willingness to apply the techniques he'd learnt and his resolve to not quit so easily play the biggest role in keeping him in the running.

Ultra instinct is the new and latest hurdle for Goku to master and he would certainly be using it as much as he does the Kamehameha.

Perhaps, the power-ups and noisy transformations are Goku's discovery of his own potential, his acceptance of his species or simply a blessing he's just fortunate to have found compared to his former martial arts rivals (Krillin, Tien, Yamcha and Piccolo). In whatever way you slice it, Toriyama-sensei aptly portray that Goku's transformations are his personal discoveries, not learnt from a master.