I'm more for the Meteor Mastermind, because of her actions for what she did. It suits her more better.
As for the teams, I have some suggestions for them (with their respective type they are spezialing; who knows maybe 2-3 types, but I stay on one type first):
Saphira's Team: Dragonite (Her ace), Naganadel, (Mega) Charizard, Haxorus, Flygon & Kommo-o
Strategy: Mostly with type coverage moves and counterattacking with (ironically) boosted fire moves thanks to the Dragon Den field
Heather's Team: (Mega) Salamence, Talonflame, Hawlucha, Drifblim, Crobat & Noivern
Strategy: Usage of Tailwind and Speed sweepers (because her team will be extremely fast and many flying types are falling in that category). I beat her mother (a former E4 member) also might had the same strategy and Heather learned everything about her
Laura's & Bennett's Teams: Lilligant (Laura's ace), Cherrim, (Mega) Venusaur, Rosenalde, Ludicolo & Whimsicott
Volcorona (Bennett's ace), (Mega) Scizor, Yanmega, Monthim, Venonat & Ariados
Strategy: I know that Laura might use a Chlorophyll team maybe, but I believe we're going to face these two together in a Double battle. So I was thinking of covering the fire weakness with rain (kinda like Shelly does), while setting up until stage 4-5 of the Flower Garden field with various moves🌧🕸
Anna's Team: Nostra the Jirachi (1st ace), Gothitelle (2nd ace), Starmie, (Mega) Metagross, Exeggutor & Oranguru
Stragety: Trick Room tactic in a Double battle with setting up the defenses and have the move Wish as well. If the Elite 4 is confirmed to actually be dual type trainers, that I would say she'll have Fairy types as well (Sylveon, Clefable and Azumarill as well.)
El's Team: Dittoceus (His ace), Smeargle, Slaking, (Mega) Kangaskhan, Snorlax and Girafig.
Strategy: I don't have a clear tactic for him, but he'll use bulk and his field to his advantage with some gimmick bullshit known as the "Fake Arceus Ditto thing". Because it boost both Normal and Psychic fields. Plus the whole Baton Pass thing
Lin's Team: Hydreigon (Ace), PULSE- Arceus, G. Gardevoir, Zoroark, Zygarde & Tyrantrum.
Stragety: Strength and power with Dark-type and Dragon-type moves, since the New World field has the most moves getting a dangerous boost. A dangerous and deadly sweep⚔
This is true because of Long Reach receives a benefit in Mountain field and technically had the Flying type until Datrix. If not pure monotype team, then a team designed around a field effect