Well, in his defense, Ash has never battled someone whose Pokémon presumably poisoned his entire team.
Paul's Drapion says hello. It poisoned/KO'd Torterra, Staraptor, and Buizel. Gliscor, and Infernape were poisoned because of the spikes as well.
I meant as in his opponent's entire team was capable of doing so, not just one of their Pokémon. ^^;
But point taken, Ash HAS battled someone whose one Pokémon poisoned almost his entire team. Still doesn't mean he can't be driven to a corner and be overwhelmed, though.