But as far as I am concerned, we rebid 1NT for all balanced hands (maybe some semi-balanced), so rebidding 1 major means the hand is unbalanced and the two suits should be as least 54 (except 1♦-1♥/♠/NT-2♣ which can be 45 if ♦ is strong enough and the hand is not enough to reverse, as we play canape for this series), which means
1. when we hold (32)44, we rebid 1NT
2. when we hold 4144, after 1m-1♥, we rebid 1♠ or 1NT
3. when we hold 1444, after 1m-1♠, we rebid 1NT
I know rebidding 1NT with a 4441 hand is not traditional, but as least the singleton is from the partner's suit which should give some guarantee and protection. Another advantage of opening 1♦ is that you can prevent opp overcalling 1♦ (though when I hold 44 minor, the possibility of overcalling 1♦ is limited)
OTOH if I open 1♣ if partner has a game forcing hand with 2 suits (e.g. 5♣/♦+4 majors) we can find a fit in minor for bidding slam. Also we could stop at 2♣/♦ for partials.
Do I missing something important that opening 1♦ is superior to 1♣ that I do not know?