I chose Flannery mostly because that was the starting point where Ash's rookie teams were starting to outright humiliate the Gym Leaders a'la how Caterpie defeated Team Rocket in "Ash Catches a Pok?mon." As bad as the win against Wattson was (bad enough that both Ash AND Wattson looked like cheaters due to the latter using a mechanical Raikou that started that whole mess with Pikachu being significantly OP even for him), I have even WORSE issues with the fact that Ash's rookie team was humiliating Gym Leaders. I could expect that kind of humiliation regarding Team Rocket, NOT trainers who during the Original series were considered very cr?me of the crop trainers DESPITE not being Elite 4 level (and for the record, it already made the already bad decision to remove Misty and force her into the Cerulean Gym seem even WORSE, since that essentially implied she's going to be a huge punching bag for rookie trainers and thus have her potential decrease sharply as a boulder off a Cliffside). Roxanne at least lost to Pikachu, an established veteran, and Brawley's pretty much the only Hoenn gym leader to actually BEAT Ash in a battle and require a rematch, so he's exempted for obvious reasons.
As far as DP, DP definitely had a slightly better Ash due to actually working hard to do things, but I'd argue it's not good enough: They still had the Gym Leaders only coming across as impressive due to Pikachu coming across as weak, despite his beating a Regice (which STILL made the Gym Leaders look bad in a different way), and don't get me started on how Pikachu lost to Paul's Ursaring despite it being one of his newer Pok?mon (and this was DESPITE Paul losing to the same Pok?mon Pikachu trounced earlier). If any of the post-OS gym leaders come across as exceptional, it's the XY gym leaders, due to the fact that they manage to come across as extremely competent in their jobs, give Ash and Pikachu a run for their money in such a way that DOESN'T make them look incompetent either, there are explicit showcases on how the Gym Leaders are skilled, and even the one instance where Ash beat a gym leader with rookies on the first try, its made clear that this was due to a self-imposed handicap on the gym leader's part. The Kalos Gym Leaders if anything came the closest to the original gym leaders in true competency.
And honestly, boring or not, I would tolerate Ash winning all the time if it at LEAST ensured that he retained his development and skillsets, rather than having all his development completely undone due to forced level resets. This isn't The Simpsons where there's negative continuity, this has a defined goal for Ash, and what I want is for Ash to actually MEET said goal.