I am of the opinion that every road leads to the same destination, but what road we each individual choose would depend very much on our own "preferences". So, in other words, I can loosely translate that meaning to our own karma, affinity and merits.
As each individual's karma and merits would vary from one another, I would imagine the same holds for one's affinity with a certain Buddha, Deity, Protector and Yidam.
Hence, which 'path' we pick would be determined by all of these.
If we have the merits to meet a Guru of a certain lineage, we must have created the causes for that to happen from previous lives. Sometimes, we may have the karma to meet but not the merits to sustain that Guru-Disciple relationship - Vajrayana.
As all schools of Buddhism teaches the same thing and the ultimate goal is Enlightenment - I seriously see no REAL sectarianism. The only bias that would arise would only come from our own minds - certainly not from the Buddha's mind or any Enlightened Beings' minds.
As we, the un-enlightened mortals hold too much duality in our perception, hence prejudices arise instead of the understanding that everything is ONE and the SAME.
Frankly, as long as we are still so attached to this and that, preferring one to other - I do not see that Buddhas and Enlightened Beings have any other choice than to emanate as many various forms and ways as possible. Otherwise, it will end up with only a small fraction of samsara's whole population who would get to be Enlightened. The rest who holds other "preferences" will never get the chance to escape this maddening vicious cycle.
I am not sure if my explanation makes sense, but that is how I would see it.
All Buddhas and Enlightened Beings emanate for our sake and hence, they have to find the best ways to reach out to us.
As varied as we are, so must the ways and the various forms - be it Guru, Protector or Yidam.