Anyone can be aware about that point of these hologram-schools. In example, inside AN 6.46 we find a discussion between 2 groups of disciples:
https://www.accesstoinsight.org/tipitak ... .than.html
this is a famous Sutta. The two groups of disciples are named jhāyī and dhammayogā according pali names. The first were cultivators of jhanas while the second were cultivators of wisdom. They kept a discussion and use different approaches. Therefore, we could infer 2 schools from there. Although it would be an absurdity because no Buddhist school existed inside the Buddha Sangha.
In example, about the Sthavira lineage (the supposed origin of the "schools" who later would conform the Theravada) the argument of being an "school" is supported in very scarce proofs. Just there is a lost text in Pasenaci language which is mentioned in another sanskrit stuff, although in fact nobody knows exactly because this is half legend. Although there is a Tibetan monk from 1.300 ace who mention this, and then we could assume xyz in order all the pieces can fit. In short, the thread is not a supposed "group of people" named the Sthaviras but following distinctive positions in doctrinal issues
Modern scholars (at least those who are not low-cost) accept the Vinaya splits like the real points of division to establish "groups". In example we can read Noa Ronkin:
this woman follows Lamotte and others who wrote the same things time ago. This is because the Buddhist Sangha was using the oral discussions after the Buddha. No written stuff existed. And this can be checked in the different Abhidhamma works, in where some take the form of discussions while others have a recopilation style. Because at this later time, the means were already available to create a written stuff, and the old discussion style together with the new one, both were registered. There is not "a new thing" neither those discussions belongs to fights between factions in where a pristine Buddhism was lost."Tradition has it that by the time the Mahayana doctrines arose, roughly in the first century BCE, there were eighteen sub-sects or schools of Sthaviras, the tradition ancestral to the Theravada, although different Buddhist sources preserve divergent lists of schools which add up to more than eighteen. The number eighteen is symbolic and has evidently become conventional in Buddhist historiography. In fact, as L.S. Cousins notes, this number is both too small and too large: on the one hand, the texts seem to struggle to identify eighteen different major schools, while, on the other hand, the likelihood is that the earliest Sakgha was only loosely organized and there must have been large numbers of independent local groupings of monks and monasteries. The ‘eighteen schools’ were indeed associated with distinct doctrinal views – often on moot Abhidhamma points – but the doctrinal opinion was unlikely to have originally caused their division. As long as distinct groups of monks adhered to essentially the same vinaya and recognized the validity of each other’s ordination lineage, movement between the groups presented no problem and there was no ground for a formal split within the Sangha. Moreover, not every school had its own distinctive textual tradition: in fact, the vinaya tradition suggests that there were roughly six distinct canonical traditions in addition to the Pali one. These are the Mahasakghika, the Vatsiputriya-Sammatiya, the Sarvastivada, the Kafyapiya, the Dharmaguptaka and the Mahifasaka."
Ealry Buddhist Metaphysics - N. Ronkin
The definitive Theravada was a conclusion of a process in a community with many people, in where the knowledge was expanded from the first times. This is a natural and unavoidable thing, it doesn't contradict the Buddha teaching.
However, the narrative of "schools" also is managed by some people like an excuse to put distance with the authority of the tradition. Then, the tradition can be show like a failed device who perverted a pristine Buddhism, whatever it can be. Here is where we could find the real utility of the toy.
Some scholars works accepts that inference mechanism in the management of those schools, while others bypass this. Others wish to detect doctrinal difference to quickly create fights between them in some Vatican intrigue style.
The Buddha had different groups of disciples under different practices and approaches. After Buddha times, those approaches evolved and new labels arose for different doctrinal trends. It doesn't mean they were confronted schools who perverted some pristine Buddhism.
The Theravada school is the historical result of what many scholars named the Sthaviras. The Theravada is at the same time the original Buddhism and also the result of an evolution. Both things. It contains the original Buddhism with different approaches already existing in the same Buddha Sangha. Like we check in the linked AN 6.46. And also it contains the stuff of the following times until the Canon was finished. The Abhidhamma explanations also is an original part of all that. If the Abhidhamma is an expansion of its original approach from the Buddha times, the same could be said about any other approach or position.
The Cannon doesn't include incompatible Dhamma views, like those about a mind arising from a brain, the non existence of kamma and rebirth, the jhanas being the only door for nibbana, the gender theory and etcetera. Paradoxically, these ideas appears under the umbrella of that new label "Early Buddhist Teaching".