What I believe is irrelevant to the issue. What's important is that the Sadducees believed Tobit was scripture, and Jesus apparently thought so, too, since His reply to them referred to it.
Currently, that is probably true. But again, irrelevant. The relevant question is whether the average 1st-century Jew, particularly the Sadducees, considered it to be scripture. Evidence says they did.I don't nor does Judaism consider it canonical.