First of all, thank you for responding to me in a constructive manner. I feel like whenever I do anything Dragon Ball-related, people either ignore me or get up in arms over what I say.
Anyway, I'll go over your arguments:
For what it's worth, Earth is stated to be at the edge of Universe 7:
So, considering inverse square law, the energy yield would surely be high enough to reach
3-A, no?
As for the Universal vs Universal+ thing, it's not really relevant to the topic at hand, but TL;DR: while we do treat individual universes as
Low 2-C objects by default, feats involving universal destruction do not and should not necessarily reach that tier because more often than not, "destroying the universe" just means performing an attack (for instance, an explosion) that spreads out across all of space and destroys all of the planets, stars, galaxies, etc. that are contained within the universe. Only when time is explicitly affected as well (whether it's shown to us in the feat itself or informed by statements) do we count that as
Low 2-C, and even then, it only counts if
all of time in that universe is affected - i.e., it destroys everything that was, is, and will be, as opposed to just everything that is at the moment of the destruction.
Reading the official English translation of these panels, Krillin said that Yamcha's idea (to leave the planet and use the Super Dragon Balls to fix everything) won't work because when Moro explodes, "the whole galaxy" (putting emphasis on this part since the original Japanese text says この銀河/“this galaxy”, or maybe "these galaxies" since Japanese doesn't have plurals, but it's not a way of saying "every galaxy") goes down with him, and that's when Tien asks "So even the Dragon Balls in space will be dust?"
The thing is, I don't think that any of these people could have known that any of the Super Dragon Balls were in the Milky Way at that moment. I know that the Super Dragon Radar is a thing and that it should be able to tell them if there are any Super Dragon Balls in the galaxy, but judging by how the scene went, it seemed to me that they hadn't checked the Dragon Radar yet and were only going to do so to try and reverse all the damage that Moro caused. If you have points against this, I'd love to hear them.
One last thing, and I'm sure that this isn't what you meant, but it's established that the Super Dragon Balls disperse throughout Universe 7
and Universe 6 after being used. This means that if one took everything liberally to claim that Moro somehow would have destroyed all of the Dragon Balls, they're likely to subsequently argue that UI Moro is
2-C, and I don't think I need to explain why that's dumb. Again, I'm not saying that I think
you believe this, but I still see this as an important detail to mention.