I’m somebody who see it as Black not turning SSJ anymore once he unlocks SSJR. This is my first real down of this so right now I have no idea why it’s done this way, but hopefully at the end of this message i’ll work it out a little more than my initial feeling.
Right, considering both the anime and manga have Black with the super duper base form, the almighty base Black is probably a Toriyama thing. Toriyama also wanted Black to have SSJ, and Rose. So basically if I tried to link these together I would just say that at one point anime Black was capable of becoming a regular SSJ too, but at some stage it was replaced with Rose once he was strong enough. In the manga it seems that we watch this progression, albeit a little sloppily as he’s already surpassed SSJB, forget about SSJG, when he becomes Rose. Even if the argument is made that Vegeta in his fresh Blue form was equal to Black, Black still must be stronger than RoF Blue, so it will seem sloppy no matter how it’s flipped.
Then there’s the link with Toriyama saying that Merged Zamasu is weaker than two SSJBs. So to combine all of these we know that Rose can’t be a multiplier at the magnitude of Blue, and instead it’s just a level that is achieved when a saiyan finds a way of surpassing ‘SSJG power’.
The manga seems to do this with Goku by having SSJG stay around, and keeping his base levels low (I dunno about Vegeta, that weird SSJ2 is something, but I’m not sure how that fits exactly yet). Black on the other hand has a super duper base, and just SSJ, or maybe he can transform into the other forms but his power is much more similar to base Goku from BoG (movie) post SSJG absorption. So his SSJ form isn’t a drastic increase at all like Goku’s SSJ wasn’t much different against Beerus compared to his base, so his SSJ2 and 3 forms would yield very little increase, and the trade off at that stage wouldn’t be worth it (as Toriyama stated in a BoG interview about them sapping strength, and Goku realised that SSJ is the right way of doing things). Then in RoF (movie) it seemed that Goku couldn’t become a regular SSJ anymore as he had that absurdly powerful base. The supplementary material, and the movie implied SSJ was a thing of the past for him.
Right, my point is that Black basically fits in line with what the movies had shown for Goku. Then there’s manga Goku, he always uses transformations as a means of getting stronger, the manga clearly never made Goku’s other forms quite as stupidly powerful as they had gotten in the movies (or the anime), this also explains Goku’s fight with Trunks, and doesn’t inflate the power scale too much in the Uni 6 tourney either.
It’s might seem like a strange way of looking at it, but for some reason Manga Base Black does seem to be more like movie BoG Goku. He doesn’t go SSJ2/3, there can be a good case made that his SSJ form isn’t the usual 50x multiplier, and later he hits RoF Goku level (this is the stage I have Anime Base Black at, not in terms of power, but his evolution) and he’s what happens a saiyan with the power of SSJG becomes a SSJ. It seems like Toriyamas second bite at the cherry for what he had originally envisioned with Goku’s strong base, SSJ being replaced by Blue, and 2-3 not being used anymore (obviously pre Blue debut, but his BoG interview did mention that Goku probably won’t use 2-3 anymore).
So yeah, this basically became a way of looking at what Black is as a whole, in both mediums.
P.S this might be a little sloppy, but I’m operating on little sleep.
