Exactly. And there is a ton of ambiguity introduced with pronouns in general, but that doesn't mean we should add to it.

And, what's worse, is that it seems the people who insist on using a singular "they" when the subject is known don't consider the ambiguity like we all naturally do with the correct pronouns.

Unless there was something prior that clarifies who the main subject is, nobody would say "Jack and John were walking and he tripped." They would say "Jack and John were walking and Jack tripped."

But it seems with the "they" non-sense, that goes out the window. You'll see people openly saying "Jack and John were walking and they tripped," not caring that it could mean any of three different things.

And the worst part is that their improper usage means my correct usage will eventually be ambiguous. Even though I would never use "they" that way, I will have to superfluously say "Jack and John were walking and they both tripped" to ensure the audience I'm not using "they" retardedly.