Misconception: Don't open 1NT with a 5-card major.
Truth: 1NT is a better descriptor of a balanced 15-17 point hand than opening 1-of-a-major.
Opening 1NT with a five-card major is the new normal. There are several advantages to opening 1NT with a five-card major (and 5-3-3-2 shape) . 1NT shows a very specific hand type: 15-17 points with a balanced hand. That is a lot more information than opening 1