Q: Is the the minor add4 chord lacking something musically that makes it rare compared to the other chords mentioned, even though it should ""theoretically"" sound just as reasonable?
A: i'm not following why it 'should theoretically' sound just as reasonable, but if you feel it has been under-used, you now have an opportunity to find and demonstrate its goodness. if you find that it really is not so good, then it is only you who can explain why you don't like it