Nobody is conflating goal arc with character arc, just you can't act like if introducing a personal conflict in XY001 and barely touching it until the Summer camp counts as "a character arc". For having a character arc, You need to address the character's problem and this barely happened during XY's first year, which is why people mentioned Serena in the first place.
That's...not how it works. And even if it
was, Serena's arc still developed in the first place. She literally goes through moments countless times where she gives up, or is forced to power through situations she would usually give up on. She has a whole episode dedicated to understanding that perhaps she thought wrong about Rhyhorn Racing. Just because every episode wasn't like "Oh, will
this be my goal?!" doesn't mean time wasn't spent on it.
The fact that her arc is literally her both searching for a purpose in life
and her overcoming her indecisiveness and quitting tendencies
necessitates that time be spent where she isn't in the spotlight.
In any case, just because she wasn't "doing anything" does
not mean there were no plans. I've had novels I've written where I've been told I didn't have a plan for a character, but I know full well I did; it just moved slowly along for a while before becoming extremely important.
I’m not even arguing with you saying that Lillie did not work…like she did not ask Ash and Nebby to transport her places to find her memory, didn’t initiate looking for Lusamine with Gladion, didn’t help Gladion and Lusamine look for Mohn and didn’t actively try to master her Z move. If you have a rebuttal against any of that argue with the SM writers because all of that occurred.
also even if I believed you majority opinion doesn’t equal the truth.
Like I said Serena did nothing before the Summer Camp arc. She left home to be with Ash, helped him develop a strategy and had that episode with Grace and moved to the background once Korrina came in. I’m not conflating anything.
Pretty sure Ash suggested going to search for her memories first in the Nebby case, and while Lillie did go with Gladion to rescue Lusamine it gets utterly undercut by both Ash being the one to end the fight and the actual resolution with her mother being offscreened (and even so, Gladion did the majority of the work in that fight, which you clearly don't accord Serena the same latitude if she were to do the same). And no, Lillie didn't even care about her father until Gladion brought it up, magically found Magearna which magically activated when she cried because
Gladion had found Zoroark. As for her Z-Move...really mitigated by the fact she was given a Z-Ring for
almost getting it right, and then we never saw her practice on screen.
And the fact you said Serena left home to be with Ash instantly invalidates your opinion when we have her literally textually stating she left home to get away from Rhyhorn Racing. Ash was the excuse she decided to use because she was fed up, not the actual reason. Holding to that perpetuated lie just shows you ignored anything that contrasts your opinion of her.
And regardless of the critique of her first year...it does not mean the writers had no plan for her. It's very
very clear that they did by how the rest of XY alone was written, from knowing Alain would be Ash's final opponent, to Froakie's arc being firmly established in XY 1, to the sheer amount of bookending between the first ten episodes and the Flare arc. You really think they'd manage to piece all of that together so tightly in advance by their own admittance yet somehow not come up with a plan for one of their major characters? Give me a break...