This raid has exposed another hole in the AI in that Primarina doesn't seem to recognize Liquid Voice Sing as being ineffective on revealed Water Absorb/Storm Drain. The rest of this post will not be about a Water Absorb user though as there's lots of coverage on that already.
https://stevecooktu.github.io/sv_raid_lookup/
The raid script shows this raid is 550 seconds or 9 minutes 10 seconds for some reason, between the usual 7m30 and 10m. The other main threat Primarina has is the shield covering 50% of its HP.
The main highlight of this post is that Marill solos Primarina too, establishing full Water/Fairy dominance. At first I thought this would be difficult due to the opening stat check of taking multiple Moonblast hits not being possible without Eviolite, which would mean not having Shell Bell healing in the endgame. I decided to roll for AI and was looking for Gardevoir's Life Dew healing to allow me to run Eviolite, but I ended up getting Sylveon + Bellibolt for maximum special damage mitigation, so I stuck with Shell Bell.
This applies to both Marill and Azumarill, but out of the natural tera options, going Fairy or Water probably doesn't really matter too much, but Liquidation has the chance of a defense drop and doesn't miss compared to Play Rough, and also resists the chance of Sparkling Aria from random double attacks though at that point it doesn't matter too much.
I ended up using an efficient strategy that saves all the initial real time wasted and gets right into the action by trying to use Belly Drum T1 and getting either Moonblasted or Sung. If I get Moonblast or Sing misses, then I can safely set an attack cheer and die on turn 2 to preserve both the offense and AI defense cheer for the rest of the battle, which fortunately cuts the timer down to right before the shield phase, and effectively gives me the bulk of Eviolite and the offense to match an Azumarill. If I get put to sleep, then Moonblast will take 2 turns to kill after the defense cheer which is not optimal but still works. Afterwards I just try to set up Amnesia and Mud-Slap again and hope for no long sleeps, but I decided to only take 2 Amnesias to save time because I could take the hits, and then just spam Liquidation as usual. I did end up using a heal cheer for a safe Belly Drum, and also late in the fight where it landed Sing on the turn I broke the shield and I just burned a heal cheer to cure it.
Overall I still don't like the approach they took here, but at least you can get around the dead time with the timely opportunity to die immediately and also preserve both cheers.
I also noticed that Primarina being able to sleep the AI also makes their potential support slightly less effective as one of the only things that actually prevents their move from going off, aside from outspeeding and KOing.