One thing I have run into lately is songwriters writing songs for other people without keeping the vocal range in mind. My wife does a lot of singer-for-hire jobs remotely online and we have run into this a lot. A man will write a vocal melody intending a girl to sing the song and he’s singing it in the key that fits his voice. When my wife hears the demo she struggles to sing powerfully in that vocal range. We end up having to change the key of the instrumental to accommodate her voice and it definitely does a disservice to the instrumental.
If you are a songwriter that writes for other singers, you must have in mind who is going to sing the song when you write the song. I know this may not be something that you want to do, but you definitely should do it. Listen to some of the work that the singer has done before you write the song. Write something that’s tailored to their voice. This same thing use to happen when my wife and I would write songs for our pop duo project. She would write verse 1 to fit her vocal range, then say “okay John you have verse 2!” Needless to say I struggled every time. We all know that melodies have to stay very similar from verse to verse or it just doesn’t sound right.