For anyone wondering, the movesets for Steven's team were:
Aggron: Heavy Slam, Rock Wrecker, Smart Strike
Cradily: Power Whip, Ingrain, Meteor Beam, Rock Blast
Metagross: Agility, Psychic, Meteor Mash, Flash Cannon (Same as in XYZ, but with Agility instead of Protect - which seems useless since it automatically gains that level of speed after Mega Evolution anyway. I suppose it's to help Metagross fight the same way in its base form.)
This episode cemented that Steven definitely deserved his ranking - his Aggron had ridiculous power and had to be disabled with Will-O-Wisp to make a big deal of Gengar's training and even then kept fighting through quite a bit of burn damage. Steven even said, " A Fire-type move...." in response, to make it seem like a big deal. But given he intended to go all the way and beat Leon, there's no way he didn't have a countermeasure against Fire-types - maybe it's just because he didn't expect Gengar to have one.
Cradily had amazing recovery and defense, plus binding, and against any opponent without a move they can release as an AOE without moving it would probably be impossible to KO. The Pikachu strategy was good, but it's hard to believe a single Iron Tail would've done the job. It might had had the most well-written moveset in the tournament, too. Power Whip lets it bind mobile Pokemon, and it can use Ingrain to recover even if they can somehow still fight back. Ingrain prevents switching anyway, so it also has Meteor Beam, which would also prevent switching while charging - Power Whip helps ensure Meteor Beam lands too. Rock Blast for emergency ranged offense. I'm actually shocked at how impressively they had a Cradily battle.
Metagross was too fast to hit at all and hit like a truck, plus had enough endurance to take 10 million volts and keep going. Again, it makes little sense a single Iron Tail would've been enough here. Having the music and audience reactions make Cradily seem really horrifying was also great since Fossil Pokemon are often like that and Cradily usually gets the short end of the stick compared to others. Still, he almost pulled a Leon and had Ash down to just Pikachu with two remaining.
Misake Iwaane posted a GIF to twitter of how he imagined the fight could go, with Pikachu trying to chase down Metagross with Volt Tackle if it still had it. The animation in it that he did on his own time actually surpassed anything seen in the battle, which is disappointing.
The pacing also felt poor since it seemed to be the reason Steven's Pokemon went down with hits that shouldn't have been enough.
If they just gave these battles two episodes it would've made it clear how hard it was to KO his Pokemon. Having 10 Million Volt Thunderbolt cut from Ash charging up Pikachu straight to Metagross dodging the beams was also a bit jarring - on one hand seeing Pikachu jump into the air can get repetitive and maybe they wanted to make it seem like it came out quick enough to have a shot at hitting Metagross, but then they should've just given Pikachu a new animation. They didn't even have the Z-Move name flash across the screen, which is customary of all of them. Really can't excuse the lacklustre animation in these battles given the amount of hype and foreshadowing they're meant to payoff, and when battles in Alola and Kalos so totally outclassed them on that front. It might be a meme at this point but it's unfortunately got some weight to it.
The cameos were also solid and having Ash directly reference Paul's training was great. Steven was also fired up at the start, saying being the strongest in Hoenn isn't enough and he can aim to truly be the strongest through the Pokemon World Championships. It even surprised Diantha, who said "This is the first time I've seen him so fired up..." Having the other Champions react to Mega Metagross was great (Diantha commenting on how hard it was to face, Cynthia saying Ash would be in for a very difficult battle against it), and so was their reaction to the Z-Move (even moreso because Steven wasn't phased until it did something it never did before and actually automatically redirected to target Mega Metagross). Also really liked a lot of Steven's lines in general, like "Whether we laugh or cry, this is the last battle!". He felt a lot fresher than a lot of the others who retreated into their stock personas.
Oh, and at the end, Steven was talking about how Cynthia would be Ash's next opponent, but that he believed in Ash and his Pokemon to find a way around her. Alain said, "Win, Ash" and Iris left with her signature "Best wishes!" Seems to sort of imply Alain and Steven still work together a bit but hopefully all of them will be back to watch the semifinals. It's also cool that even after seeing Cynthia VS Iris, Steven still felt Ash could beat her. Not sure what that says how what Steven felt his odds would be - at the very least I imagine he sees her as an equal. It was nice seeing him and Iris together too - still, Iris interacting with Lance was missed out on and she didn't talk to Steven or Alain. But knowing they all get along well is nice, and having them - including Steven specifically - cheering for Ash, even when there are other Champions present with ties to them really does feel like he's earned their respect and support in ways the others haven't.