As has been mentioned before, post-Zamasu heal Goku Black would start the chain of characters being 2-C anyway, as SSJ Goku Black clapped SSB Vegeta and would be 50x his base.
In addition, I'm not entirely convinced of some of the evidence, given that SSG being vastly above SSJ3 doesn't really prove anything on its own. Even a 2x gap can canonically result in a stomp in Dragon Ball, so a good chunk of this evidence really doesn't hold up when taking that into account.
The Resurrection F point, which seems to be the largest crux of this argument, doesn't exactly hold up either. If your interpretation was the case, why would Super Saiyan God ever come back as an actually used form? Since, in that case, it would not actually provide any boost. The whole "god-like Saiyan" thing, just like in the anime, is a matter of having that level of power and then being able to go beyond that. Given that this promotional material also very strongly follows the movie and anime versions of the arc, their base forms being 2-C would make the most logical sense.
I was initially going to be neutral, but having typed all this, I actually talked myself into another stance. I disagree with the OP