The manga kept the fusion-boost the same.

[Fantastische Hure]

Or at-least similarly huge.

I don't know how that can be seen any other way.

 

[Papasmurf]

Merged Zamasu got a shit boost tho

 

[Fantastische Hure]

Merged Zamasu got a shit boost tho

Or not. Goku-Black and Zamasu were already significantly inferior to Vegeta and Goku respectively, so it only makes sense their fusion gets owned by Vegetto.

 

[Papasmurf]

SSJB Vegetto > Beerus >>> CSSJB Vegeta/Galu ~ Merged Zamasu while Black wasn't inferior enough to Vegeta to be defeated very quickly so I'd say the boost was lower overall.

 

[Let's Go Fearless!]

Goku and Vegeta are in the same level while Future Zamasu is even weaker than Future Trunks, that's why the product of Merged Zamasu is not as strong as Vegito.

 

[Fantastische Hure]

SSJB Vegetto > Beerus >>> CSSJB Vegeta/Galu ~ Merged Zamasu while Black wasn't inferior enough to Vegeta to be defeated very quickly so I'd say the boost was lower overall.

Future Zamasu was much lower than any of them, though. The CSSjB might just be that huge.

 

[Pyro]

Future Zamasu was weak as shit, weaker than the Super Saiyans. Dude was like the Kibito of his fusion.

 

[Void]

SSJB Vegetto > Beerus >>> CSSJB Vegeta/Galu ~ Merged Zamasu while Black wasn't inferior enough to Vegeta to be defeated very quickly so I'd say the boost was lower overall.

Vegeta and Goku get a rival boost too. Zamas dragged Black down too much.

 

[Fantastische Hure]

Yeah, the manga >>> anime.