That's sort of my point though. Goku can't know exactly how strong someone is without fighting them. Same goes to Zamasu in that instance. It doesn't only apply to special techniques that don't involve powering up. (Such as Hit's Skip)
Oh you mean how Goku went down from SSB to SSJ. If he knows he can overcome Zamasu's power in SSJ then it's better that Goku go down to SSJ to take care of it so he had as much power as possible for Black, especially considering how much of a problem the manga makes out SSB's power drain. He was walking but that doesn't mean he's not badly beat up/weakened from the attack, it still put him in base form from SSJ. He had mad battle damage after that and was walking with his arm held.
When Goku used the "mastered SSB" form, he was in perfect condition. Goku wouldn't be able to use it nearly as effectively anyway in a weakened state.
Goku's Kaioken activation was still instant, when comparing it to the U6 arc where he powered up for a minute, drops it altogether, then powers up again and being excited that it worked. That's a pretty big difference in accustomization. (yes that's a word i looked it up)
He usually has a clue. If he didn't know what Zamasu could do, he should have used one of his lower Super Saiyan forms, like Super Saiyan God he loves that. Yet, he starts at full power and powers down in the middle of the battle, which I still don't understand why he did it.
He should have stayed Super Saiyan God Super Saiyan simply because he suffers a massive energy drop like Vegeta did against Hit. So he wouldn't be good against Black since he would be basically like Vegeta fighting Hit. And since he fought Zamasu, he should know that his Super Saiyan form was weaker than him since Zamasu is at least within the range of Super Saiyan 2 Trunks who is equal to his Super Saiyan 3. I mean, why not used Super Saiyan God or even Super Saiyan 2? Why did he drop all the way down to Super Saiyan?
Since he only need to attack Black once giving how massively powerful that form is, he wouldn't need to be in prime condition. The same with Merged Zamasu round 1 where Goku was trying everything he could to beat Merged Zamasu, yet didn't think to used this form. Remember he didn't know about the time limit.
Beint instant doesn't mean there were no risks just activating it. Just the the odds were higher than 10% and he didn't need to charged it. It could have been even money as far as we know, but the fact that Goku didn't used it until he was nearly disabled is telling.
The fact is, if Goku gave an explanation as to why he waited so long to used this mastered form, it would have worked better, much like what Goku did against Hit. It could have been as simple as, "This form is far from perfect and I could die using it, but now I have no choice". Instead we get a line about Goku's body breaking after he used it for several minutes. Which is why the question "why didn't he used it sooner" is being asked.
Nah, I don't think so. You're list sounds about right to me and that is pretty much everyone. I'm not sure your reasoning helps your argument at all. To me, you simply listed a bunch of names that can counter SSB. Thank you for making my point.
The manga has Trunks at the proper level. He can match SS3 but, can't go any higher. To me that comports with his current situation of having no training partners with the exception of Kaoishin. Also correct me if i'm wrong but, it took Vegeta years just to get to SSJ2 and Goku just as long to get SSJ3 (which he did not perfect right away). So I can see four years and still having some issues with a new form.
The anime is trying to sell merchandise, so I guess it would make sense to have as many forms as possible.
There have been a lot of characters introduced in Super and that list is far from everyone. That is like saying everyone in One Piece knows Haki despite it being limited to a few dozen characters with a series with hundreds of named characters.
Out of the five member of the U6 team, only Hit competes with Super Saiyan God Super Saiyan.
Goku Black and Future Zamasu were the primary villains of the Future Trunks Saga, with one of them using Goku's own body against him.
Tournament of Power: Out of the characters from the exhibition matches, only Toppo is on Goku's level and he wasn't even officially part of the roster.
U7 team: Only Vegeta, Gohan, and Android 17 are on par with Goku out of nine other people.
The manga has Trunks stronger than he should be since he's only has Super Saiyan 2, yet is able to challenged Super Saiyan 3 Goku. Anime Trunks couldn't do that, was weaker than Super Saiyan 2, and only got so strong thanks to Super Saiyan Rage. And taking years getting a form doesn't mean it takes years to master it, especially a form that is build on being calm and having great energy control. When Goku wanted to master Super Saiyan, he did it in less than a year and we don't know how long it took Vegeta to get Super Saiyan 2. We also don't know how long it took Goku to get Super Saiyan 2 and 3. On top of that, Super Saiyan God Super Saiyan is literally just basic Super Saiyan with god ki. It isn't even a new form, which makes even less sense for them to take so long to master it.
This isn't about merchandise, especially when the manga made Super Saiyan God Vegeta a thing and is still using Super Saiyan God Goku and even had him used it in his Resurrection 'F' outfit, while the anime didn't.