Never said it was the same, just similar. Proto-Slavic and Proto-Baltic both originated from Proto-Balto-Slavic, which says something, no? A common origin before the split that would occur is a logical conclusion, which when attention is given to the similarities of both groups, such as case forms and other such things, actually start to put your protests to becoming moot. Both the Baltic and Slavic languages are very archaic and far more so than any other Indo-European language group(s). Both share features that no other languages share in the Indo-European language family. I’m not saying that they are the same, but that they very possibly came from the same thing. You have as much proof as I do for or against the existence of the Proto-Balto-Slavs, but that’s what we get for delving into a theory that may never get past being a theory.