Personally I feel like the Relationship between Lusamine/Lillie made it up for me even though that is clearly an unpopular opinion.
Like it or dislike it, you gotta admit it had some issues. Putting aside the fact that it's a poor adaptation of the games for a second, the relationship itself is somewhat inconsistent. When Ash meets Lusamine for the first time, Lillie's shown to hate her mother's over-affection, finding it embarrassing and somewhat condescending. Then, a few episodes later, she's shown to dislike it when her mother doesn't shower her with affection due to being busy with work. So, she hates it when her mother is too affectionate towards her, but she also hates it when her mother isn't paying that much attention to her? Now, I know that these two are (somewhat) extreme cases and that Lusamine should balance her work and family life better. But the way Lillie acts' hates her mother fro these petty reasons and doesn't even try to understand her a little isn't good. Combine that with some of the stupid things she says, like hating how Lusamine evolved her Clefairy into a Clefable despite Lillie's "entirely logical conclusion" that Clefairy was cuter (God, i'm never gonna forget that stupid scene), and Lillie really comes off as a jerk for half of the Aether arc.
And then there's all the problems that come from it being a poor adaptation of the games. The main one being that, despite completely changing Lusamine's character, the writers still decided to incorporate elements from Sun and Moon's story with little to no alterations, even though most of them hinged on Lusamine's insanity. Gladion believes that Lusamine knew about Lillie's "accident" (and was, thus, partially responsible for it) and chose to leave his family with Silvally, even though Lusamine had been shown to be a caring (though occasionally neglectful) mother who would never do anything that would put her children in danger, making his decision to leave very questionable. Lusamine still has an interest in Ultra Beasts, but instead of coming from a desperate desire to find her missing husband, it's just because her father told her stories of these things, making her "obsession" with them shallower. Lillie still dresses in her Z-powered form, but, since she doesn't do it as a sign of her growth as a character and her becoming her own person, her new costume comes off as nothing more than fan-service of the empty kind (even more so since it's abandoned by the end of the arc). And then there's also the fact that Lusamine and Lillie's relationship doesn't change after this arc, despite it being portrayed as not being a good one. Despite the arc ending with Lillie starting to admire and lover her mother more, the next time they had a more meaningful interaction during the Necrozma arc, Lillie complained that she has barely seen her mother outside of work, while episodes after that arc showed that she was still over-affectionate towards her children (to the point that she managed to embarrass both of them in front of the entire Alola region during the league) and still treated Lillie like a baby. So, basically, nothing changed in their relationship? Despite a major point of the Aether arc being how Lusamine being too focused on her job and her treating her children like babies was a problem? Even though one of the last scenes of the arc showed their relationship changing for the better?
And these are just the problems that come form the change to Lusamine and Lillie's relationship and the former's overhauled character. There are a lot of other issues that this arc has (form major ones (like the classmates barely interacting with Nebby even though they supposedly bonded with it), to more minor ones related to particular episodes (like Nebby being able to teleport Lillie to places from here childhood that she doesn't remember, even though it was established that Nebby teleports people based on what they're memories and what they're thinking of)). In the end, this ain't that great of a story arc and should not be used as an example of how future arcs should be. If anything, this should be an example of what not to do in a story arc moving forward: don't cram the entire story of a game in a 12-episode arc, don't change some elements of a game's plot while leaving the ones that were linked to those altered elements unchanged, don't have the arc focus on an important character's growth and/or the evolution of their relationship with someone and then ignore them.