Let me clarify briefly on the previous post I made about the contemporary "Leggiero Tenor."
Vocal fachs are ~kind of~ made up. A master singer can sing anything from high tenor to baritone!
There are clips of Adam Lambert (while still having a light instrument) singing more like a "lyric tenor" in a musical theater context. A BIG part of "fach" that many classical singers get wrong is that it's technique based. It's how Domingo went from singing baritone to tenor in the middle of his career! These differences are amplified even more when you introduce a microphone and contemporary genres into the picture!
For that reason I personally prefer to think of a voice as being either "very high, medium, low, and very low." So, for example, Adam Lambert is an example of a "very high tenor." Placido domingo is an example of a "high baritone/low tenor." It gets rid of a lot of the confusion associated with the traditional idea of "fach."
What matters isn't what "fach" you are, but how you're pronouncing your vowels!
Let's say you're a "medium tenor" (a classical lyric tenor)
If you modify toward OPEN vowels, you can pass for a "baritenor" in musical theater circles. An example of a singer like this is Leo Norbert Butz. Notice how all of his high notes modify toward a manly sounding, chesty, open UH.
If you modify toward CLOSED vowels, you sound more like a high pop tenor. Justin Bieber, for example, modifies towards the closed, heady "Ooh" vowel. Justin Bieber modifies the phrase "All I need is a beauty and a beat" to "Oohll ooe nooed is a boohty oond ooh boeat."
Don't get me wrong, fach is important. A low bass will never sing a high C5 like a high tenor. However, much of the differences between fach can be nullified with diligent practice, masterful execution of technique, and vowel modifications!!!
Hope this helps!