Headcanon
The non-canon personal ideas, opinions and believes that certain person or group of people feels strongly attached to, about a certain work of fiction (book, movie, cartoon, anime series, manga, comic book, etc...)

Sometimes people put their own headcanons above the actual canon of what was actually shown.
Person A: Android 17 is barely SSJ3 level, and that is exaggerating! Goku in SSJ Blue could have defeated 17 with a single punch!

Person B: That is your Headcanon. If he is a SSJ3 level character, then why Goku fought 17 with SSJ Blue instead of SSJ3, like he did with Trunks in a previous arck? Also, how can a SSJ3 level character resist attacks capable of hurting SSJ Blue evolution Vegeta and SSJ Blue kaioken x20 Goku that are 20 times more powerful than a SSJ Blue, 17 received a kick from Jiren, meant for Vegeta Blue Evolution in episode 127, and also took an explotion from Jiren that was able to knock out Goku and Vegeta, and he was still able to fight, a SSJ3 level character shouldn't be able to do that!