A lot of Ash's reserves are getting minimal screen time and many of the rivals are being treated like crap, but do you think their current treatment is enough for them to be considered decent battlers? If the saga were to end right here, do you think Ash's Boldore would go down as a powerhouse in our memories or as another poorly treated reserve?
Burgundy lost all of her on screen battles, but if the battles are actually examined instead of just paying attention to the end result maybe she's not such a lost cause after all?
In her battle against Cilan, her Dewott actually did pretty well. It wasn't dominated by Dwebble. Dewott would have one-hit KOed Dwebble with Aqua Pulse if not for Sturdy provided that it works the same way it does in the games. And it was after Dwebble's Shell Smash that Dewott fell (I don't think anything has survived Dwebble/Crustle's Shell Smash yet) Dwebble's such a powerful pokemon that it earned the nickname Zeustle on these forums, so holding it's own against a pokemon like that is pretty impressive. Her Sawsbuck fared a bit worst and was kind of demolished by Pansage.
In her battle against Ash her Stoutland actually put up a decent fight against Palpitoad. Palpitoad went on to defeat a pokemon that swept three of Bianca's pokemon soon after.
Dewott failed again against Iris, but put up a decent fight. Iris vs Burgundy is probably one the my favorite battles in Best Wishes. It wasn't short and brushed under the rug like many other battles in this saga. Excadrill seems like one of the strongest members of the main cast and had already beaten over 100 pokemon before that battle. Dewott actually seemed to be even with Excadrill fr a while. Pretty impressive.
And Burgundy vs Trip was an abortion of a battle. Darmanitan falling to an attack it had resistance to in one hit makes it her weakest pokemon in my opinion.
So for Burgundy her Dewott, and to a lesser extent Stoutland, may actually be competent battlers. Her other two (if they're ever even seen again) need work.