There are a small number of artist agencies in the US (Columbia Artists Management) and in Europe who do the basic decision making about who gets work, who gets promoted and who doesn't. I remember that there was a book in the IU library with the German and Austrian agents' names and addresses. When you go to audition, it's for them and not for anyone actually hiring. When you listen to recordings and go to performances, you are hearing this screened set of performers.
In their minds Tristan has a certain sound, as does Isolde, Contessa Almaviva, Tosca, Mimi, Octavian, Don Giovanni, etc. They are comparing the auditioner with these preconceived voice types. What this means is that they all end up sounding the same. Then they go on to work with the same coaches and conductors who also have their preconceived ideas.
To break through this standardization process and achieve a truly creative, individual performance is practically a miracle. Only the recording companies provide an alternate path. Don't give up the struggle. Art is in the individual vision.