In case B, shouldn't both types from Salamence be SE against Venusaur? Dragon isn't, so it's not viable as a choice.
When I said that it was not the most logical choice (to which I see you were offended) I meant that if both directions work, the players have more choices and thus the chance to come with more creative sets, which more often than not are the winning ones as everyone will expect the usual trios. I also believe that if a pure type is weak to both types of the previous and SE against the following it could be included. An example is a trio of: a pure Fighting, a Psychic/Flying, and a Dark/Ice pokemon, which as a trio fits the criteria.
In my opinion that could also be a possible choice, but I am not the one making the rules.