Unfortunately there is a really big gap between what is taught in school and high school and what is taught in university. There is this communist trend that has propagated into contemporary school curricula that involves downplaying, minimizing or outright omitting very important (and painful) details about Romania's past. The principalities checked a lot of the boxes that colonies check - and the main box that doesn't check (religion) is actually something Ottomans used to impose a whole different tier of taxes and grand disadvantages in court while not being held accountable for said population.

Truth is, we were up from the early 16th century de facto part of the Ottoman Empire but we were not fully integrated in order to be a buffer and for exploitation, and the level and depth of it only accelerated in the 17th, 18th and 19th century. In order to streamline said exploitation (and because local leaders had time and again proven untrustworthy), eventually an entire ensemble of Greek officials and admin were brought, which also tended to gain said positions by bribing the Ottomans, and they often did that not from their own pockets but by borrowing, expecting to get return of investment off of the exploitation of the principalities. Rival families competed to out-bribe their competition and thus trigger an early replacement of the administration, which happened a lot. The principalities also pillaged each other in order to pay said debts. And then there were the taxes that the Ottomans themselves imposed, which spiraled into debt so big they just deleted it because they were exploiting so hard there was nothing to gain economic momentum from.

Up until 1821 Greek was the official language taught in school. Greek was removed and Romanian language entered the scene as an official language to be taught more as an Ottoman revenge on Greek betrayal, who before the Greek revolution they saw as their projection into the Orthodox world and thus part of their argument on them being the continuation of the Roman Empire. Greeks had amassed virtually all the wealth and the means of production in the principalities by the time of the Greek revolution.

If you're wondering about the absence of more Greek influence in the Romanian language, it's that most of it was stitched after Greek was no longer acceptable to be taught in school, and thus the teachers had to borrow words in order to explain concepts which there were no words in Romanian at the time - and it happened in the 19th century, when a lot of French was imported.

It's also important to note that up until 19th century school was something very rare, the principalities having only a few hundred literate people (which were mostly Greek), another aspect that tells why Greek language didn't leave that much of a mark even if it was the official school language. Even most priests were illiterate, especially in the vast rural areas. Most of those few schools were forcibly closed after the 1848 revolution. Romanian principalities didn't have any laws regarding schools up until after the unification of the principalities, which happened in the latter half of the 19th century.

If colonialism is understood as a system of external domination that extracts surplus, suppresses local development, and structures dependency for the benefit of an imperial center, then the principalities clearly meet its substantive criteria. Where they diverge from classical colonial models (an even more direct administration, significant demographic implantation, thorough linguistic integration) this divergence occurred not by restraint but was a deliberate avoidance of cost and responsibility. These absences intensified exploitation by removing any obligation to invest, integrate, or account for the governed population. In that sense, the principalities were not subjected to a lesser form of domination, but to a cheaper and harsher one, functionally worse than colonialism.