A difference with Lillie and Gladion
One thing I think about with these two are how Lusamine potentially raised the two of them.
It is sad to say that I think everyone can relate to feelings of your parents manipulating your own choices in life to match their own will…
One thing that gets to me is how Lusamine herself treated UB01 and Type:Null. It is possible she could have easily projected this on her children, prompting Gladion running away years earlier.
UB01 - Powerful by sheer existence. The ultimate beauty. It has no will of its own, so its own will is reflected from its host.
Type:Null - An experiment created to fight the ultra beast. Keeps its helmet on until it fully trust someone.
So my idea would be along the lines of Lillie facing worse emotional trauma because Lusamine would be trying to zap her of her own will. Gladion left the foundation woth torn clothes from Null, so it might be safe to say he had more physical neglect tossed at him, even if he wasn’t meant to fight the ultra beast.
If this is the case, it is easy to understand why Gladion left so early.