There are a lot of questions in your post but most of them are extensions of the first and so don't really need a separate answer.
Q: Does Buddhism consider itself to be the one right religion, and all the others wrong, like how most religions approach other religions?
A (mine, anyway
): Not to anywhere near the same extent. Buddhism is internally more pluralistic than most religions and (partly for that reason, I think) externally more tolerant. Buddhists tend to think that good ideas are good ideas regardless of their source, and that most religions have good ideas in them. Consequently ...
Q2: If only Buddhism has all the "right views", then doesn't it make sense to say "Buddhism is the one true religion, and all the rest are invalid"?
A2: No. It makes much more sense to say all the rest are somewhat valid.
As for your last question, this particular Buddhist can't begin to imagine anyone capable of "believing in, deliberately and firmly, non-Buddhist religions, including all wrong views therein, and also expounding those views" because that would involve believing in a hundred conflicting religions at once.
But if you mean someone simply believing and expounding any one religion, I would probably accept that they are doing the best they can with the knowledge they have been given, but gently discourage them from thinking they had the only
right answers and an obligation to convert the rest of us.