I've played Middle Cup a lot in the past, and personally, I enjoy the Eviolite-less meta more than the Eviolite meta. Middle Cup is more suited as an offensive tier rather than a bulky offensive, stall-ish tier where you have to boost up to +4 to OHKO things.
There are a lot of great Pokemon in Middle Cup. Croconaw is amazing with Life Orb + Swords Dance / Aqua Jet / Waterfall / Return - just like Feraligatr in RU. Piloswine makes an awesome Choice Band user with its 100 base Attack and Earthquake and Ice Shard attack. Seadra has the ability to sweep with Hydro Pump / Ice Beam / Hidden Power Grass / Agility. It's surprisingly bulky for a sweeper. Combusken is a great late-game sweeper that can 2HKO almost everything in the tier, but it has to watch out for Aqua Jet's from the likes of Croconaw and Wartortle. Dusclops is a great tank with Will-O-Wisp / Pain Split / Earthquake / Shadow Sneak. Porygon2 is an excellent tank as well that is very versatile and bulky. It even has Recover! Choice Scarf Magneton is probably the best Choice Scarf user in Middle Cup - if not the best.
My favorite Middle Cup Pokemon set right now is
Rhydon
Trait: Lightningrod
Adamant Nature (+Atk, -SAtk)
- Rock Polish
- Earthquake
- Stone Edge
- Swords Dance
Probably the best sweeper in Middle Cup. It's extremely bulky (physically bulkiest Pokemon of... Pokemon with Eviolite attached), has incredibly high Attack that will OHKO most Pokemon without boosting, and one of the best STAB combinations. The only things wrong with it is its mediocre defensive typing and low Speed, but that's not that bad when you compare it to all of Rhydon's boons.
Anyways, if you're having trouble making a Middle Cup team, some of these Pokemon would be good to start out with. There are many other good Pokemon such as the Dragon-types, (I really want to try out Shelgon sometime, although it's probably outclassed by Fraxure as bulk barely matters in Middle Cup...) Kadabra, Haunter, and Electabuzz. It's a very fun tier; if anyone wants to battle, feel free to come onto #othermetas and ask for a battle. I'm down to battle most of the time. Just note that I won't be on there much the next few days because of finals, but a few people who frequent that channel have played Middle Cup before.