In the interests of clarifying my use of terminology.
Any existing teaching which was not specifically classified by the Buddha as Dhammavinaya had to have been created or spoken by someone for it to come into existence.
By teaching from outside the established Dhammavinaya and the Four Great References, yet at the same time springboarding from it and claiming allegiance to Buddhism and refuge to the Buddha, lineages established themselves apart from Dhammavinaya as sects. The sum of Dhammavinaya and all sects constitutes Buddhism.
Since there is no Buddhist lineage which adheres solely to the Buddha's Dhammavinaya and the Four Great Reference - they are all by definition sectarian, thus sects.... and that includes Theravada too. (Relative) orthodoxy or majority rule doesn't grant immunity from being a sect, nor does being the one to have deviated the least distance. A sect cannot become unsectarian unless it removes its sectarian additions and returns to a pre-sectarian state (i.e. Dhammavinaya).
As to value judgement on sects, that is for the individual to decide for themselves in accord with their own reason. I do not believe terms like "Early Buddhist Sects" are inherently value laden.