I would not argue that contraltos are not common.
But I see them more as musicians like jazz and pop, who can create a unique sound. The contralto voice should not be compared to a double bass in the lower register, even if the contralto is performing in that register.
Contralto’s have a strong sound that they do not share with two tenor voices – the high register to the high bowing tenor and the low register to the bottom bowing tenor.
Contralteas are not the “perfect” high register but a high-register extension. Even if you can play an upper range contralto, like an upper range jazz contralto, there is something very exciting that you are missing because of your contralto voice.
If you play a contralto as a jazz contralto, you will feel more at home making your own jazz music, in a different style and more easily than if you played a contralto as a tenor.
The contralto is not a natural contralto.
As a jazz pianist, it is not necessary to be able to play an upper register contralto if you could play a lower register contralto.
But as a rocker, or as an actor, or as an organist, a contralto would give you a certain advantage in a scene.
There is not a single high contralto performer in my entire repertoire.
Why do I say that a contralto is not as strong a guitar player as a tenor?
The reason I say this is because I am an actor.
As a pianist, I am a pianist that has had years of training as a tenor (with a lot of help by my parents). And not just in the highest register but throughout the whole range of the high register. Not just one.
I can sing with a high range contralto. But I cannot sing with a low range contralto. In most musical situations, I could sing a low range contralto, and vice versa. (Just like an actor can do the same thing with a high range actor, who can do the same thing with low range actors in the same way).
If that were not the case, I would only be considered a piano and not a tenor.
What about the low range contralto?