In a 40 year history of singing lessons I have had both types of teacher
1 Singers who teach tend to judge you by their voice - which can be difficult - my last teacher had a lower voice than me and this limited me at first - they also work on the repertoire they know which meant for me Wagner - this was fine but I like singing verismo My first tenor teacher was the late great William Macalpine who basically made me a tenor and pointed me toward the lyric repertoire
2 Singers who teach also this problem - rivalry - I had a bigger voice than my last teacher which caused some jealousy and I went to a famous ENO baritone when I was singing Tonio and Alfio 30 years ago He was an actor singer and did not like it because I belt out the Gs and A flats easily
3 Singing coaches are more dispassionate
In case you are wondering "If he is so good why is he not at the Garden etc " Factors are
1 I did not become a tenor until I was 38 - 9 Too old for professional work My voice did not settle down until I was in my 50s By that time I had a thriving marketing business - a wife and a mortgage
2 I am really very ugly I have had my share of rejections by fluttery little opera directors (and a few sopranos)

A great face for radio I think is the expression