I do the Team Magma quest and obtain a Chinchou with the following IVs:
I train it against some Water trainers, Abandoned Ship, and the Water route before it (I had them left so decided to use them anyways) and it reaches level 36 before entering Seafloor Cavern. I reach Archie with the following team:
Team: Lanturn(37), everything else(43)
Mightyena: Very luck based. His Mightyena goes down if Swagger is merciful on you. Crobat, not minding potions, is 3HKOed by +1 Shadow Ball, but also has Confuse Ray. Sharpedo is OHKOed by +3 Strength, since it swaggered it. But yeah, very luck based.
Nosepass: HStone Rock Slide is a 2HKO on Crobat. This is the most reliable win for this fight, even though it can get screwed up by Confuse Rayas well. HStone RSlide is a 3HKO on Sharpedo, but Swagger.
Machoke: boosted -1 Revenge OHKOs Mightyena if it doesn't go for Swagger. Normal Revenge OHKOs Sharpedo. Crobat is no. Keep in mind Sharpedo also tries to Swagger you.
Xatu: Psychic OHKOs Crobat and Solar Beam OHKOs Sharpedo. Don't go against Mightyena unless you like playing on luck.
Lanturn: Mightyena is pretty much RNG fest with the Swagger, but, not considering potions, Surf is a 3HKO. Crobat and Sharpedo are 2HKOed and OHKOed by TBolt, respectively, though Crobat can ruin your day with Confuse Ray. Sharpedo here went for Slash directly instead of Swaggering, but I can see the danger of Swaggering.
I make it to Juan, with levels being virtually the same, bar Lanturn, as I had to pour in all the Gym Trainers into Lanturn.
Team: Lanturn(41), rest(43)
Mightyena: bad matchup. +1 Shadow Ball 2HKOs only Whiscash and Luvdisc, with the latter being annoying with Sweet Kiss and Attract. The rest are 3HKOed and in most cases beat you, as Juan likes to heal them.
Nosepass: lol
Machoke: Sets up a Bulk Up and can spam Revenge. If triggered, Revenge will be at least a 2HKO on everything. Discounting confusions, Machoke will be able to sweep if you heal it at some point (in my case, I could have won by healing after taking down Kingdra).
Xatu: Does very well. +1 Solar Beam 2HKOs Kingdra and OHKOs the rest. Kingdra is the only thing that's really threatening Xatu, as its Ice Beam is a 2HKO. Luvdisc is annoying due to Attract + Sweet Kiss. You will have to reset up Sunny Day, but if it's not against Kingdra, it's not a problem. Good matchup overall.
Lanturn: Like most Electric-types, Lanturn doesn't deal well with Whiscash and Kingdra, but the rest are 2HKOed or OHKOed by Thunderbolt. Beware the Luvdisc, though, as it's faster.