On the 400, the spinny exit is a good foot higher on the mast – keeps the asymetric away from the forestay.
Whether the 2 holes for the 400 jib makes the mast weaker or not, I don’t know. But no 400 masts go at the hounds – if they are going to break its gooseneck or spreader bracket: and normally they go because something else has given way or applied too much pressure (shroud, kicker, halyard tension, mast ram etc.).
The 2-1 will reduce the tension on the halyard, and therefore help rather than hinder the strength??