It's just such an utterly negligible thing in the grand scheme of things, oh no Serena wasn't creative in dealing with the minor plot device characters that largely have nothing to do with her character, what a terrible thing.
Like who cares really? I don't even remember the "creative" TR encounters most if the time because their TR battles, which are always just filler to pad the episode out, always. Very rarely do they ever have dramatic or narrative weight to them so who cares if Serena dealt tm with them easily, I have no clue why you're so obsessed with this one incredibly minor thing
They're the minor plot device characters that largely existed as the twerps' main opponent, which was the main problem for a lot of the pre-BW episodes. There was no need to go back to that problem, especially since XY touted itself as an
action series more than any previous series. Hell it wasn't just a downgrade concerning TR, BW for all it's flaws tried harder to downplay the whole plot armour and easy victories for the twerps, they even called out fluke wins as shallow for once. XY was a complete remission of that, they didn't care how the heroes won so long as they did and superficially looked badass.
To go into this without it turning into a TR thread, Serena, even if a great character, was a lousy action protagonist, because even besides TR, she won everything easily or through cheap plot device. There is no emotional investment in a character that wins EVERYTHING without effort, especially since it's hard to display their defining positive talents in a situation any imbecile could win in. Look at the Flare arc, it was the big finale arc that was supposed to show everything the cast had learned and grown, etc. Serena barely had anything to do, they tried to tout her as being able to stick up for Maron but she was incompetent against even grunts and needed saving all the time herself, largely because she'd spent the whole series never improving in capability. Oh she was being nice and motherly and meant well, like she wasn't that at the start of the series. You say it doesn't matter, but why shouldn't it if 1. it's an action series and for all intents wants Serena to be an action protagonist and 2. they still wanted to overlook this error and give the idea she IS getting better (albeit badly) thus making the whole story look pretentious and badly written?
I agree they should have been developed better, but how would TR contribute to their development at all?
By using them more than just as plot devices and making their face-offs challenging enough that they developed from them?
Hell just downplay them for other challenges and rivals. It only sticks out because they would rarely have them deal with anything else. Even in the showcases, Jessie was by far Serena's most prominent opponent. It was lazy. They just wanted Serena to have a straw loser to make her look superficially better. The other Pokegirls had TR as well, but not JUST them, they got GENUINELY better.
