I still have the postgame to finish.
Edit: finished the Rainbow Rocket story, surprisingly didn't need a second shot at Giovanni, but needed it for Ghetsis and Cyrus.
Edit 2: beat all the other postgame trainers, including the Elite 4 and Hau again. I'll battle the E4 again and see if I can beat the other challengers.
It took multiple tries against the Elite 4, for some reason I couldn't replicate my initial success against Molayne, Olivia, and Acerola. With the first 2, Excadrill swept, utilizing Rapid Spin and Swords Dance to make it a sweeper. For Acerola, it was Sticky Web from Ariados, and other team members getting KOs thanks to the speed drop. Kahili, I lost the first attempt, but figured out how to take her out, having Meowstic set up Nasty Plot on Skarmory and get an early lead, then have Milotic finish the match.
For Hau, Sticky Web again, the sweep came in the middle of the match. Milotic burned Azumarill with Scald, and Meowstic got switched in to set up Nasty Plot and destroy the rest of Hau's team, including his Mega Salemence, who used Dragon Dance instead of hitting me. First attempt at Hau by the way.
I don't use healing items or those X items during battle. Hold items came in handy: Quick Claw for Ariados and Incineroar, Weakness Policy on others, Air Balloon on Excadrill. I made sure none of my Pokemon went past 2 hearts, I saw how broken 3 hearts was, and I couldn't tolerate that. I didn't use Z-moves either. When I first got the Firium Z, I played around with it, but for major trainer battles, I didn't use any Z-moves.
It was pretty grindy for me, mainly because it took a long time to form my team and the hack makes it feel necessary to have a full team as early as possible. The Lucky Egg alleviated the grind, that was my only major complaint about the hack, thankfully taken care of. Yeah I loved this, but I'm used to playing hacks at breakneck speed on an emulator, taking 2-3 days. Using my 3DS, even with the movement speed and text speed increased via patches, this has taken over a week to finish. The SOS chaining and EV grinding took up a lot of time.