There actually was a strategy that BP was helpless against - SwagPlay. Funny how both are relatively non-interactive strategies (BP only cares about boosting up until Stored Power/Hyper Voice KOs everything, SwagPlay only cares about Confusing/Paralyzing the opponent until they either kill themselves or they're taken out by Foul Plays) but where BP works by skewing the odds entirely in their favor, Swagplay wins against them by making luck the *only* important factor.
Not exactly. BP had a winnable match-up against Swagplay because of Magic Bounce, only having Special Attackers with no Atk IV's which made Foul Play much less effective, and the fact that more than half of the team members carried Substitute to put a massive damper on the Parafusion aspect of the strategy, which Swagplay almost completely revolved around. Towards the end of the test, Swagplay was less common to see than Baton Pass because of how much more reliable it was as a strategy and the fact that it had this decent match-up against it. The BP player could lead with a physically defensive Espeon with 0 Atk IV's (Foul Play couldn't break the Sub), put in a Substitute, and then pass into Scollipede to start gaining Iron Defense boosts to make the Subs basically unbreakable for Swagplay via Foul Play from that point onward, or just Calm Mind up on the spot and dent the Swagplay team quite easily. That said, Swagplay certainly tried to adapt to BP by including things like more Prankster Taunt users and sometimes even a standalone sweeper of their own like Mega Pinsir, and the BP player always had to be very mindful of Ditto, which could come in whenever a Sub wasn't up, copy their boosts and either pass them on to another member, or try and counter sweep if enough boosts had been obtained.
To be honest, I thought this time in the meta was actually interesting to watch, play and construct in, and the creativity and counters that were being conjured up during this time was pretty damn interesting to behold. We saw a lot of Stall teams popping up because of how good they were against the standard Swagplay teams since Chansey was virtually untouchable, could pass essentially free Wishes and had Seismic Toss to always break Subs. Then we saw Swagplay start to include things like Gothitelle to break through this idea, then Shed Shell Blissey became a thing (kind of like what happened in Ubers this gen because of the presence of Mega Gengar), who could switch directly into a Pursuit user like T-Tar (who resisted Foul Play and had Sand Stream to cancel their Lefties and give them passive damage behind their Subs). Creativity and team building options during this time was arguably higher than at any other point in the game, and the fact that the meta wasn't so streamlined in terms of the strategies and pokemon that were viable gave it a nice element that we don't see as much of anymore, so there certainly were positives.