What about
- architecture (The classical one, not Romanesque architecture)
By the Late Empire, the classical architecture had given up to a late imperial architecture. Long story short : more massive buildings made of bricks.
The few remaning buildings from the era, most were replaced by newer ones as for what concern Roman buildings (go in any Italian city, you won't find much ancient neighbourhood : even "medieval" centers were mostly re-build in later centuries), are generally continuing the style and knowledge.
I mean...look at your point : Early Middle Ages didn't continued
classical architecture. You could as well argue that Romano-Barbarians didn't spoken a
classical latin, therefore not being acculturated.
- technology (running water, aqueducts, concrete)
Ah, concrete. It never fails to appears as the last argument of "Barbarians ate my Romans"
Concrete use was eventually abandoned even during Late Roman era : it was expensive, required some technicality and material found essentially in Italy (use of concrete elsewhere is much more restricted)., and was essentially used for massive buildings.
Eventually, using abandoned suburbium was clearly easier and cheaper.
The recipe was known : it's written in Vitruvius' treaty which was copied since Early Middle Ages. It wasn't used (at least during a period : we know some concrete was used in medieval Italy at lest by the XIIIth).
I give you that the immaterial technology was lost, lack of transmission : there's certainly a difference in quality between building teams that are used to a certain material and keep memory on how to use it, and taking it from a book.
But that's the lot of technologies that get abandoned (for good or less good reasons) with time (a bit like many stone work was better in the XVIIth or XVIIIth than in the XIXth in Europe)
And even if it was lost, like a poor ark, how exactly would that point that Barbarians weren't hugely romanized?
I think you're cheery-picking stuff that have nothing to do with basic cultural structure there. (I don't think you're saying concrete is an essential part of romanity, isn't?)
Aqueducts remained in place after the Vth, but became indeed less used as they cost a lot to be repaired : even Byzantium had trouble repairing his own after Avar destructions.
It was just cheaper to just let it down , critically giving it ceased to be widely used due to demographical changes (loss of population, new centers of population even in ancient cities, etc.)
It's not a problem of lack of cultural assimilation or Barbarians being Barbarians, but about societal changes due to crisis that Europe had to wait centuries to really get out.
I would point, again, that you're mentioning feature that concerned maybe 10% of the Roman population. Do you really think this make it essential for Roman culture?
- knowledge (different historic and other works lost during late antiquity)
Which is irrelevant to the cultural continuation and assimilation, unless arguing every book made the Roman culture (in which case you can write off 95% of the population of Romania off the Roman culture)
- administration (except the churche, there is no centralized administration until the 17th century)
Romano-German kingdoms largely maintained Late imperial administration which was everything you want except centralized : while you had a personified rule, the basic administrative and political structure was the city (understood first as a municipe, then as the seat of a count and bishop after the IVth in most of Romania).
You're basically projecting a modern conception of state into Roman Empire, anachronically so, in order to point a cultural difference that I'm afraid to say so again, didn't really existed.
- political unity (compare 4th century Europe and 18th century Europe)?
Did you even took a look at Late Imperial civil wars, split of Romania and various usurpers?
If something, VI/VIIth Europe may have been somehow stabler than the Late Empire.
So, in fact, a partially assimilation of the conquerers occured, but not a full romanization.
But, according your choices, romanisation means being exactly like Roman elites and having EVERY of classical features even ones that weren't widespread in all empire.
At this rate, nobody was romanized, not even Romans.
More seriously : when institutions, material culture (the everyday stuff), the language, the beliefs, even arts are in the same continuity...Well, yes, you're facing a same
culture and that's obvious once you take a look not at the classical culture of the Ist century, but at the actual Roman culture of the IVth/Vth century.
There, I'm afraid to say, I think you're writing off all the evolution that happened within the Roman Empire between the Ist century and the Vth century as if it never happened or shouldn't have happened : a bit like if one argued that because Indian immigrants aren't speaking Shakespearian English, that means they're not assimilated to the
true English culture.
Great parts of Roman culture
Which you didn't really gave exemple for, I'm afraid : you just mentioned either vague or irrelevant points, when you gave exemples that you cherish in Roman culture but aren't representative either historically (meaning up to the Late Empire) or socially. In short, I think you have an elitist view on culture.
this never happened in China.
Think of XIXth/XXth crisis in China, and all that was lost and you may have an idea of what Late Romania looked like in terms of structural changes and losses.
We could count all the damages caused by Mongols in China similar to what they caused among the Arabo-Islamic world, including cultural (part of pre-Mongol litterature for exemple) and technical losses (advancies into hydraulical technology).
It's not the same extent, but saying it never happened in China is blatantly wrong and serves only an obsolete narrative.