I don't know how to tag, so this will have to do.
This goes back to teambuilding: Some teams are successful while others are not due to a plethora of reasons. If one's team consistently loses, for whatever reason, then the player has to--or rather should--edit the team to deal with what threatens it. This is a fact of competitive Pokémon. Though you do need a good match-up against BP, as you say, the same can be said about
any teams, not just BP teams. This is another well-accepted fact of Pokémon.
Also, more than HO teams can fit Talonflame and M-Pinsir. Such conjecture is grossly oversimplifying their utility. Furthermore, more than those two can adequately deal with BP. I used one example because of convenience.
Regarding leading with Vaporeon or Zapdos first,
prediction is a core part of Pokémon, and you conveniently forget this tenant. Because of this, the player should, in addition to having Talonflame, have an answer to Vaporeon and/or Zapdos on his/her team that works
outside of beating Baton Pass (of which there are plenty). As I said before, it is all about effective teambuilding
in addition to effective
prediction. Remember, it takes two to play Pokémon; one player is not doing all of the predicting. That is grossly oversimplified.
If any member of a BP is wasting a turn setting up Agility if Scolipede has gone down, that is a turn that s/he can be hit, and many Baton Passers are frail (except Gliscor, but there's HP Ice for that). If Scolipede is gone and the opponent sends out Zapdos and or Jolteon, s/he will have to choose between Substitute or Agility. That is not a good position for the player to be in considering s/he will most likely get hit.
For Iron Defense, any team should also have Special Attackers, instead of only Physical Attackers; otherwise, the player has no means to effectively deal with it. For BP teams, accumulating Special Defensive boosts is more difficult than accumulating Defense.
Also, in order for Sylveon to effectively used Stored Power, she desperately needs to be passed Defense boosts, for she is way too physically frail, and any smart player should not let those boosts be passed to her.
All in all, this all goes back to effective
teambuilding and
prediction. If something you are doing is not working, then you have to change it. The same X will always result in the same Y. The community needs to start thinking of creating solutions to what we're seeing. Like with any team, you have to consider what your threats are and what counter-measures your opponent will use. This is common sense.