While I do agree that BP needs a nerf, I think you're exaggerating how hard it is to beat a BP team just a little. Talonflame, Landorus-I, Thundurus-i, and Charizard-Y can handle BP before a sub is put down. However, they can't always beat BP, and once the chain is started its nearly impossible to stop even with these pokemon. Beyond that, its a stratagy that almost takes away the importance of strategy and decides the game based off of matchup. Its for those reasons I think it should be nerfed.
I do believe those pokemons are extremely good counters agianst some of their leads but talonflame or mega char-y get put to sleep to a focus sash smeargle leaving them useless, then a freeturn to get an speed boost or something like that, only extremely fast taunters can get a hold on this especially thundurus, and sableye (the secnd being on uu), also i would like to mention that being around 1500 elo i had seen like 8 or 9 tpeople using this strategie making it quite anoying