Honestly people are talking up the rematch teams, but the first battle teams for the gym leaders aren't bad at all, they are greatly improved all around and keep in mind all of these below have EVs now and good natures as opposed to neutral ones and most of them have items now when before they did not.
-Roark's Cranidos gets Bulldoze to screw over Monfernos
-Gardenia's Turtwig gets a Miracle seed and Work up instead of withdraw and her Roserade gets Technician to hit harder instead of natural cure as well as Petal Blizzard instead of Magical Leaf
-Mayelene's Meditite gets Light Clay Light screen to set up as well as Bulk Up instead of meditate, Her Machamp has Low Sweep and Knock off instead of foresight and leer and an Expert Belt and Her Lucario has an Energy Root to make Drain Punch super annoying and Bulk Up to set up
-Crasher Wake has a Damp Rock Quagsire to set up his Swift Swim Floatzel
-Fantina's Drifblim has Will'o'wisp Hex combo and Strength Sap to make it annoying as hell lol, Gengar has a Colbur berry to stop dark attacks and isn't running a physical set unlike DP lol, Mismagius is mostly the same but with an expert belt
-Byron has Bronzor set up trick room now for his slow mons, His steelix has EQ now and replaced Ice fang with Thunder fang for water types, his bastiodon is still bad lol
-Candice's Snover has an Icy Rock for hail, her sneasel is a meme pickpocket set lol, Her Medicham gets rock slide for flying types and has an expert belt, and her Abomasnow gets Aurora Veil as well as EQ, Giga drain and Blizzard
-Volkner has a Shuca Berry Raichu with Surf for coverage and volt switch, His Ambipom has the anti fighting berry, his Octillery has an expert belt and a focus energy sniper crit set and his Luxray has intimidate and steel and ice coverage
For the E4
-Aaron- Dustox has Black Sludge and Moonlight for recovery to toxic stall better, Beautifly has Wiseglasses to boost Special Attack and Quiver Dance to set up, Vespiquen has Sitrus berry and Acrobatics, Flame Orb Guts Heracross with Facade speaks for itself lol, Drapion has Night Slash and EQ now alongside Scope Lens Sniper.
- Bertha's Quagsire has Water Absorb, Leftovers, Toxic and Recover on her Quagsire(annoying as fuck again lol), Her Sudowoodo has Rock Head Head smash with a Sitrus Berry, and it has EQ now, Golem has a much better set with EQ and Stone Edge and Heavy Slam with brightpowder, Whiscash has Rindo Berry Belch combo, and her Hippowdon is Chesto Resto with 3 attacks(sidegrade here)
-Flint has Wide Lens Hypnosis Rapidash with low accuracy high power moves, Life Orb Sheer Force Steelix, Minimize Will'o'wisp, Baton Pass unburden sitrus berry Drifblim(kill me lmao), A Lopunny set with more than just Fire punch to attack like HJK, and his Infernape has iron fist focus sash now.
-Lucian's Mr. mime has Filter now to reduce damage alongside Light Clay Dual Screens and STAB, Muscle Band Medicham with great coverage, Sap Sipper Girafarig with Trick Room, Bronzong with Trick Room and 3 attacks with a Berry(seems to run a lot of low speed natures to for the trick room portion of his team) and he has an Alakazam with Life Orb and Magic Guard.
-Cynthia's 1st team- Spiritomb has a Sitrus berry and sucker punch/Shadow ball now, Roserade has an expert belt and better coverage moves, Gastrodon has Storm Drain and Leftovers and Scald, Her Lucario has a Nasty Plot special set with Wiseglasses, Milotic has Flame Orb Marvel Scale with recover and good attacks and of course the Yache Berry SD Garchomp
TLDR: Game has much better teams even in base game