It's a gimmick episode and it belongs as a "one-off" in the middle of a season. As an individual episode, it would have been harmless enough. I imagine the script, or something very much like it, had already been written and was either shelved or waiting in line to be filmed at some point and Braga/Berman et al. were just too lazy and arrogant to write an original script because they didn't see the point in writing original material for a cancelled series so they picked this one off the cutting room floor and reworked it to shoehorn it in as the finale.