I dont mind about SM since it is trying to do something new in the anime so we should give it a try, but how was XY series stale, ash had a gym quest had best battles in the series history, even the pokegirl had her own active goal which made things more interesting, also different arcs least amount of fillers of all. I dont think XY series was stale at all, lol the most overrated and stale series has to be OS, especially the johto region, fillers after fillers, misty and brock doing nothing and becoming background characters, no progression of storylines between two gyms which keeps the story interesting, gary hardly appearing at all even though he was supposed to be his main rival.
SM has its flaws but i think it has given some ideas which could be carried forward in gen 8.
XY gotten stale because of everything about Ash, being stripped of his personality and turned into a mary sue that everyone glorifies. While the series still uses the rinse and repeat formula that we seen enough already. Most of his pokemon besides Ash Greninja and Pikachu were underused in focus time. (Name anything Noivern has done to earn his evolution.)
I already got on with Serena and why her character arc was ANOTHER problem but let me put this into context.
I made a fan character that left home because she didn't want to be bound there. (This case, it was because she hated everything about the Orre Region "Play Colosseum and XD to have an idea why someone would hate growing up in that place." and wanted to fulfill her goals out of that dusty place.)
Kind of shows up out of nowhere for a main character. (Because the Orre thing was background information and I didn't have much plans with her until I was focusing on another characters arc.)
Has a goal that kind of changed over the course of her story. (She wants to be a news reporter and didn't take the job because she was too young. Her journey took her from Johto to Unova... where she became a movie star at PokeStar Studios. She still wants to be a News Reporter, but what she obtained with the show business is actually something nice to work for in the mean time.)
Doesn't battle often or even at all compared to the actual battlers of the cast. (The girl has quite a few pokemon to talk about. A Glaceon "Starter.", a Granbull, a Durant, a Heatmor and the reason she is able to pull the flight option so well ;an Alakazam with teleport for when the trainer or her friends get into a situation where fighting wouldn't go so well. Due to a growing conflict and a danger... that is very much something that exist in the real world. "Spoilers" She had a wake up call to get serious with battling when she discovered she and her pokemon are targets and knows using teleport to solve her problems isn't going to work forever... especially since shadow tag exist!)
In addition since I realized those pattern way late into making her arc....having boy problems. (A guy from Sinnoh that came to watch his father at the World Tournament. Those boy problems however... came after the girls break point in her carrier as a movie star and at no point does her goal revolve around that crush. "Quite the contrary it was that crush that helped the boy's family overcome MAJOR issues." To add to the boy problems, both her and the boy has some actual chemistry going once all is said and done.)
All of this are plot traits of a main character in a piece of canon poke media, who in the span of three seasons has went nowhere with her growth. Compared to a fan made side character, in a fanfic, that has those traits of her character/growth and generally has done much more!