Sure, he has, but you'd hope he'd consider that kind of logic.
I'd have thought he'd keep Pidove. The only time he didn't have a bird on his team was Orange Islands & early Johto, and even then he still had a Flying type. They like him having Flying types so they can scout things out. When you say performing badly, do you mean she's not good in battle or she's not popular with the audience?
Bulbapedia seem fairly sure he still has Zuruggu. They only list Ash as having Pikachu, Zuruggu & Sewaddle on hand, with the others listed under with Juniper, accompanied by an explanatory note.
I'd hope he'd be logical and send Snivy off...but who knows.
But yeah, his sixth Pokémon bar Pikachu...let's consider how long it took him to capture his other sixth Pokémon...
Krabby in EP013, so earlier, but fairly close.
Let's count Johto separately. Phanpy hatched in EP228.Johto started in EP117, so it took 111 episodes.
Aipom was caught in AG179, not even in the right region.
And Gible was caught in DP157.
So it's closest, really, to Krabby. After Krabby he wet on to catch Muk, Primeape & 30 Tauros before his Kanto journey ended, not to mention Haunter, or Snorlax & Lapras in the Orange Isles.
Incidentally, they're moving through gyms quite quickly aren't they? Can't help but wonder if there are any post-Unova plans for Best Wishes...