Riolu's evolution in this episode marked the first time since Sinnoh (Quilava) that a pokemon Ash has caught has evolved in a different region that it was caught at, and the fourth overall (the others being Donphan and Sceptile). Though for older viewers, the Ash/Rose fight gave off BW-vibes considering Riolu evolved mid battle and finished off two pokemon, and remember in BW when Kotetsu's Riolu evolved Ash only had Snivy and Pikachu remaining, and also like in BW the move that ended the fight was Aura Sphere. I did like that Lucario used its aura to communicate with Ash.
Onto Go's fight, I can translate what Olena was chatting mid-battle:
Oleana: "Useless. I'm amazed that you thought you could stop Eternatus, as weak as you are."
What Oleana actually meant: "Useless. You thought you could beat a Water-type with a Fire-type."
As for the fight, it was nice to see Go take advantage of the narrow hallway to attack from all angles, not giving Milotic enough time to dodge all of the attacks. And with Cinderace beating Milotic with Pyro Ball, Go now enters the pantheon of characters who beat a water-type with a fire-type (a club that Ash and Gary are a part of). Despite having other moves at its disposal, I'll give Go a pass for wanting to use Ember to finish the fight as that is the move at the heart of Go's/Cinderace's development as of late.
Moving on to the meat and potatoes of the whole shebang, the Eternatus fight. Despite the fact that Team Rocket got their obligatory blast off, Mewoth at least attempted to use G-Max Gold Rush, keyword being attempted as Mewoth reverted back to normal before the attack could finish, and barring Night Slash (which he claimed to have in DP), this is the first time Mewoth has used a new move since EP008. The fight itself was nothing out of the ordinary as far as the plot is concerned (one difference being Leon using an Ultra Balll in the episode as opposed to a Poke Ball in the games), though I wasn't expecting Go to be the one to capture Eternatus, sure it was sealed away in a safe but the data is still in his pokedex, but I think sealing it away is the right call imo.
All in all, I do think that the pacing for this episode seemed too quick considering the amount of content crammed into this episode.