I do agree that her 'redemption' was done pretty sloppily, but it's not like that's the reason I like the character. I would've have liked her just as much if she had stayed bad until the end.
That was probably why USUM made the changes it did with her to try and clarify something or why we had the Anime not make her evil period but still a lousy parent that is responsible for her kids problems. (Flat out neglect.)
They tried to make a villain/ antagonist that we want to see redeemed in the end and they pretty much failed in S/M due to a few things I see wrong, including ending the plot right there when it should have continued.
(And before you say USUM should have been a sequel or DLC, most of the story in the first game would have never worked as one due to how Lillie and Nebby became attached to you and dumping all that on a new protagonist would result in B/W2's problems happening. With DLC... Necrozma showing up after the Beast Clean up killed the chances of that revolving around him.)
Though if you want to be technical, what Lusamine ended up becoming in USUM is generally a more villainous Zinnia instead of the other villains. A woman that became crazy with grief, done villainous things for a greater good while under the delusion they are the big hero. (They are anything but that!) When really their actions nearly doomed everyone.
Lusamine's actions resulted in agrooing Necrozma, Zinnia's resulted in the earth being exposed to an large oncoming meteor. (This lady was the reason Archie and Maxie got the idea to wake up Kyogre and Groudon in the first place... pokemon that would have caused the apocalypse.)
It makes Lusamine a weaker villain in USUM... but to me it makes her a better character.
At the moment IMO... the manga is kind of disappointing me in a lot of things.
(Lillie contributing less to the main plot in the grand scheme of things than the anime and USUM. "The game where she loses focus." Dare I say besides letting us know a few things about her and adding PTSD from the abuse done to the girl, she has zero development by this point. In addition, we have no Mina showing up, a lot of things being rushed. "No totem Kommo-o" No frozen pokemon scene, Hau contributing nothing compared to the games and the second Cosmog that comes off as an ass pull and dampers Lillie's hiding Nebby thing that was seen in both games.)
The S/M Manga is starting to drop things and it has one more year to make things interesting again because I seen Pokemon Adventures go above and beyond in this. (Gen 1 and 2, the first two generations had next to no plot in the games or the anime, so the manga made something from that.)