dir() will get me TracebackException as a name, help(traceback.TracebackException) will get me its signature. IDEs with autocomplete and signature tooltips will do the same.

There is nothing in those usage sequences to say "don't use __init__, use this redundant class method with the same signature instead".

I agree providing a "directly from an exception" constructor is essential for cases where you're working with a caught exception at the Python level. I don't agree with the idea of duplicating the required low level API under a different name so it doesn't *look* like a lower level API in the documentation.