I read this thread before heading to Akuwa town, so good looking out. Val has been tough for me on most playthroughs, but thankfully I could catch a few pokemon before we're locked out of the mainland. For those of us playing on normal mode, the advice about not using grass types isn't as helpful; normal mode Val uses a Seaking that proves to be truly problematic for most electric mons. If you're reading this for help on a normal mode play, go ahead and embrace a bit of grass.
My team that eventually won wasn't very good:
Cinderace
Gloom
Lurantis
Floatzel
Swoobat
Electrode
I started with Swoobat, as when it knows psychic (lv 41 - rare candy) and has full health, she will switch qwilfish out (it wasn't afraid of confusion lol). Dewgong would be a problem for most of this team, as it's very bulky and, once it gets stockpiles + rest going, can't be penetrated. Swoobat with simple helped though, as I could get to +4 spdef spa really easily. I needed most of the team to hold a persim berry (which we just got from the shore) to avoid whirlpool ruining things. Swoobat needed 2 psychics at +4 to beat dewgong, since it comes with a spdef boost on the switch. Cinderace behind electrode's light screen beat primarina with headbutt flinch spam. After every KO she threatened me with qwilfish, but Swoobat kept forcing it out and eventually beat it with a single psychic. The main reason gloom is here is to get a stun spore on qwilfish, to neutralize its swift swim. Couldn't have won without that. Lurantis handled floatzel, seaking, and Lanturn, but it did die in the fight as a pivot, so I needed a max revive. That makes me feel like I didn't "really" beat Val, but she's tough. I'll take it. I tried a zebstrika, no good. Electrode was gonna be the ace here, but couldn't fight with Seaking lurking around.
Now I gotta figure out how to make my trash mons get through Geara. Feels like I need EV training to go any further.