I decided to get Seel right after beating Morty. After that, I tackled the Team Rocket Hideout before going to Chuck. This is not really optimal, because it basically means I had to cross route 41 SIX times, but I think it's the most fair to Seel.
My thoughts so far.
Noctowl: it hasn't impressed me so far. It has decent bulk, but it can't really make use of it because it has severe power issues and it doesn't have very useful support options either. I can see it in D for now, but if it does well at the E4 I might consider C.
Venomoth: the Venonat stage is pretty bad, but it tinted lense STAB sludge bumb does really help. It has decent power and sleep powder, but its mediocre stats and bad typing hold it back. Will probably end up in C.
Primeape: another C tier probably. It has decent speed and good attack, but it's not actually that powerful because it doesn't have very strong moves. Still, it does have good coverage which makes it a decent route cleaner.
Dewgong: it comes kind of late, especially for a water type, but STAB ice type moves are very useful. Its offensive stats are lacking, but it does have access to some good moves like surf. Matchups have been so-so. Will probably end up in either D or C, depending on how it does at the E4.
Noctowl (30): specs confusion is a 2HKO Primeape. It's only a 4HKO on Poliwrath, counting the sitrus berry. Poliwrath can't use hypnosis on you thanks to insomnia, so it will never hit focus punch. This allows you to just truck through with confusion, though you may need a potion. Good matchup.
Venonat/Venomoth (30/31): venonat fails to even 2HKO Primeape with specs psybeam. Venomoth on the other hand, can outspeed and OHKO with specs psybeam, though this is a range. It's a 3HKO on Poliwrath. You might need to use an awakening, but it's still a pretty good matchup for Venomoth.
Primeape (29): karate chop is a 3HKO on the opposing Primeape, so you just need to get lucky to beat it. You can use taunt to make this more consistant though. Vital spirit protects you from hypnosis, but Poliwrath overpowers Primeape anyway. Screech makes karate chop a 4HKO, but you'd be lucky to live long enough to survive that long. Overall, decent matchup.
Seel (29): specs surf is a 2HKO on Primeape. Poliwrath utterly walls Seel though. Mediocre matchup.
Venonat/Venomoth (30/31): venonat fails to even 2HKO Primeape with specs psybeam. Venomoth on the other hand, can outspeed and OHKO with specs psybeam, though this is a range. It's a 3HKO on Poliwrath. You might need to use an awakening, but it's still a pretty good matchup for Venomoth.
Primeape (29): karate chop is a 3HKO on the opposing Primeape, so you just need to get lucky to beat it. You can use taunt to make this more consistant though. Vital spirit protects you from hypnosis, but Poliwrath overpowers Primeape anyway. Screech makes karate chop a 4HKO, but you'd be lucky to live long enough to survive that long. Overall, decent matchup.
Seel (29): specs surf is a 2HKO on Primeape. Poliwrath utterly walls Seel though. Mediocre matchup.
Noctowl (30): I mean, reflect is kinda useful against Steelix, I guess.... Terrible matchup
Venomoth (31): even tinted lens can't make Venomoth be able to hit steel types with sludge bomb. Specs psybeam is a 2HKO on Magnemite and a 5HKO on Steelix, counting the sitrus berry. Venomoth also have stun spore and sleep powder support. Mediocre matchup.
Primeape (29): karate chop doesn't OHKO the Magnemites, but dig does. Steelix always sets up sandstorm on turn 1, so you can bop it with a focus punch if you have the move slot for it. Screech turns karate chop in a 3HKO. Smart use of screech can allow you to bypass the sitrus berry too. Good matchup.
Seel (30): it doesn't OHKO the Magnemites with specs surf, and it gets OHKO'd in return by thunderbolt. Steelix struggles to do damage to Seel though, and surf is a 2HKO against Steelix. Kind of a neutral matchup, I think.
Venomoth (31): even tinted lens can't make Venomoth be able to hit steel types with sludge bomb. Specs psybeam is a 2HKO on Magnemite and a 5HKO on Steelix, counting the sitrus berry. Venomoth also have stun spore and sleep powder support. Mediocre matchup.
Primeape (29): karate chop doesn't OHKO the Magnemites, but dig does. Steelix always sets up sandstorm on turn 1, so you can bop it with a focus punch if you have the move slot for it. Screech turns karate chop in a 3HKO. Smart use of screech can allow you to bypass the sitrus berry too. Good matchup.
Seel (30): it doesn't OHKO the Magnemites with specs surf, and it gets OHKO'd in return by thunderbolt. Steelix struggles to do damage to Seel though, and surf is a 2HKO against Steelix. Kind of a neutral matchup, I think.
Noctowl (30/32): specs uproar doesn't even come close to 2HKO'ing Seel, so you really have to have air slash to even stand a chance. Specs air slash 2HKO's Seel, 3HKO's Dewgong and 4HKO's Piloswine. Noctowl can't take more than two ice type attacks though, so needless to say, Noctowl is definitely not going to sweep here. Mediocre matchup.
Venomoth (31): 2HKO´s Seel and Dewgong with specs sludge bomb. Piloswine is a 3HKO. Piloswine 2HKO´s with ice fang though, so you can´t beat it without healing. Decent matchup.
Primeape (31): karate chop is a 3HKO on Seel and Dewgong. It's about a 5HKO on Piloswine because of the sitrus berry, but screech can turn it into a 3HKO though. You can abuse focus punch if you predict the AI to use hail. Overall, it's a decent matchup, but Primeape is too frail to sweep consistantly.
Seel (30): specs surf 2HKO´s Piloswine, even counting the sitrus berry. Seel and Dewgong wall it. Mediocre matchup.
Venomoth (31): 2HKO´s Seel and Dewgong with specs sludge bomb. Piloswine is a 3HKO. Piloswine 2HKO´s with ice fang though, so you can´t beat it without healing. Decent matchup.
Primeape (31): karate chop is a 3HKO on Seel and Dewgong. It's about a 5HKO on Piloswine because of the sitrus berry, but screech can turn it into a 3HKO though. You can abuse focus punch if you predict the AI to use hail. Overall, it's a decent matchup, but Primeape is too frail to sweep consistantly.
Seel (30): specs surf 2HKO´s Piloswine, even counting the sitrus berry. Seel and Dewgong wall it. Mediocre matchup.
Noctowl (36): specs air slash doesn't even 2HKO the Dragonairs. Gyarados and Kingdra totally overpower Noctowl. Pretty bad matchup.
Venomoth (36): Gyarados and Kingdra outspeed and overpower it. Specs sludge bomb is a 2HKO on the Dragonairs. Mediocre matchup.
Primeape (35): it can take out either Gyarados (with screech and rock tomb) or one of the Dragonairs. Kingdra just OHKO's it. Pretty bad matchup.
Dewgong (36): Gyarados and Kingdra are too bulky for Dewgong, though you can try to get lucky with sheer cold. Specs blizzard OHKO's the Dragonairs though. Decent matchup.
Venomoth (36): Gyarados and Kingdra outspeed and overpower it. Specs sludge bomb is a 2HKO on the Dragonairs. Mediocre matchup.
Primeape (35): it can take out either Gyarados (with screech and rock tomb) or one of the Dragonairs. Kingdra just OHKO's it. Pretty bad matchup.
Dewgong (36): Gyarados and Kingdra are too bulky for Dewgong, though you can try to get lucky with sheer cold. Specs blizzard OHKO's the Dragonairs though. Decent matchup.
My thoughts so far.
Noctowl: it hasn't impressed me so far. It has decent bulk, but it can't really make use of it because it has severe power issues and it doesn't have very useful support options either. I can see it in D for now, but if it does well at the E4 I might consider C.
Venomoth: the Venonat stage is pretty bad, but it tinted lense STAB sludge bumb does really help. It has decent power and sleep powder, but its mediocre stats and bad typing hold it back. Will probably end up in C.
Primeape: another C tier probably. It has decent speed and good attack, but it's not actually that powerful because it doesn't have very strong moves. Still, it does have good coverage which makes it a decent route cleaner.
Dewgong: it comes kind of late, especially for a water type, but STAB ice type moves are very useful. Its offensive stats are lacking, but it does have access to some good moves like surf. Matchups have been so-so. Will probably end up in either D or C, depending on how it does at the E4.