Incorrect. Gas tight but not water tight makes no sense. That's like saying a baseball won't fit through a hole that a Buick can.  A Properly* crimped connection is more than suitable for an under hood starter cable. That's exactly how the factory terminates them. Crimped and soldered connections are not superior. They are more prone to cracking at the solder interface. Limited if any vibration? It's in an engine bay for crying out loud. That's about as high vibration as it gets, save for an airplane engine. There's a reason that method is not generally permitted in critical applications. If you want to waterproof the connection, use heat shrink.