I think that you're thinking too narrowly here - and too recently.
Some examples:
The original sect was (IIRC) a jewish messianic apocalyptic sect. Was changed to include gentiles and allow non-adherence to jewish laws.
Major differences between 'originals?' and gnostics.
Adaptations to facilitate adoption by roman empire.
Partial agreement of beliefs not until 4th century - but other branches/sects held to their own views.
Great Schism about 1000 years ago between RC church and Orthodoxy (still exists and keenly felt). Orthodox churches believe RC church left the truth.
Divisions within Orthodox church re autonomy and within RC church re papal succession.
And all of that's before we get to the precursors to protestantism, 500 or so years ago.
It's a similar situation in many religions. Buddhism, for example ( a much older religion) and islam (a much newer one).