that's not even true, whether you're talking about story titan, or hm titan, or titan x
you can easily recover from losing a dps (my first titan x kill we had 3-4 deaths throughout, still managed to meet the dps checks)
to be fair though, there are quite a few openings where you can lose a tank/healer and still have time to rez them and recover
but.. if a tank or healer eats a landslide, that's almost always a wipe, a dps though? yeah you can 7 man titan x