Even if you try to phrase it as "welp, they were banished", that doesn't change the part where they were "banished" for actions of a single individual. Even by your own admission. And Jaina simply gave no shits about whether it was a single individual or not and conducted no investigation whatsoever, so I'm not sure where you got the "Aethas refused to give names" part from. She asked for no names. She went back to Dalaran (from doing more or less the same thing she accused Blood Elves of), killed 5 guards before she even said anything about banishment, Purge or even your names, then did the rest. And given how she did that behind Council's back, she had no right to banish them anyway, which means Aethas had all the right in the world to refuse to accept her nonsense. Then conducted the Purge with foreign troops.