Honestly, it feels like there is too many mental gymnastics to justify Zamasu not being 2-C. You have to assume so many things.
Why is Future Zeno less caring than Present Zeno? Because of Goku? Let's go back over what the Grand Priest stated.
- "Zeno-sama foresaw this outcome...that the warrior standing at the end, would be virtuous enough to consider other universes."
- "If a selfish wish had been made, he would have erased everything."
Now, the only part that indicates Zeno has 'changed' is Whis stating:
- Perhaps Zen-Oh sama has expectations. That Goku and friends can change something. That mortals can change."
However, this is logically inconsistent. We know Zeno was planning to hold the Tournament of Power because of Goku vs Hit entertaining him, but Future Zeno had no such impetus.
It is, however, stated that Zeno had intended on erasing the 'lesser' universes so he could manage the 'greater' universes easier.
Does that mean Zeno doesn't care? On the contrary, no.
Zeno's first appearance in the entire series is him checking on Universe 7 and 6's performance.He wanted to ensure the Gods of Destruction were managing their universes properly.
Zeno's entire impetus for wanting to destroy the lower 8 universes was:
- A) Because the Destroyers were doing a poor job
- B) He wanted to redirect his energy towards the Destroyers doing their jobs properly
Not because he wanted to erase all existence or that he 'didn't care'.
So why did Zeno hold the Tournament of Power? Simple. He saw Goku and Hit fighting, and believed mortals still had potential. His gambit was to test the virtue of mortals from the worst universes and to see if they had power, and the virtue to use that power properly.
With the above in mind, why would Future Zeno erase every single universe in the future? It's completely OOC for Zeno to not care about the universes. It's OOC for Zeno to erase all of the universes, because he clearly wants to put effort into them and it's OOC for him to erase the universes due to a god running wild. His entire reason for erasing the lower universes was to make it easier to manage the higher quality universes.
So overall, it's OOC as hell for Future Zeno to erase all the universes. The only thing that changed with Present Zeno, meeting Goku, is that he wanted to give the lower universes a chance. Zeno's care and management of the multiverse has always been a major part of his personality, long before meeting Goku.
So either:
- Future Zeno saw no more worth in the multiverse
- Future Zeno erased Infinite Zamasu, and erased the multiverse as a result of Zamasu being the multiverse.
We know Zeno highly values the multiverse, wants to develop it further and his reasoning for erasing the lower universes was so he could manage the higher universes better. Zamasu essentially completed those goals for him, so there is no reason for Zeno to erase them.
Thus, the latter must be correct. Zeno erased the multiverse because there was no other option to defeat Zamasu.