Man.... I chose a bad time to let the muses take control of me!!! SO much I missed in this thread.
Let me start with this:
It's very difficult from an archaeological/historical standpoint to truly state the claims above. While, yes, we do have evidence of Christian marauding of pre-Medieval sites throughout Europe and Asia... we also have concrete evidence of preservation within the same area. Many Christian churches and cathedrals were built on top of earlier, non-Christian edifices throughout the Middle East and North Africa by the Romans, Byzantines, and later kingdoms. Further, we see many non-Jewish traditions incorporated into the Christian theological practices that many scholars often wonder if Christianity is instead based on many of these pagan traditions.
I would argue that -regarding the mayhem mentioned in your second paragraph- that this was less due to Christianity and more due to the fact that a strong, centralized governing body gave way to a series of ill-conceived and short-lived polities that resulted in the populace lacking basic needs. The result was a breakdown of society that resulted in a turning away from the perceived indulgences of antiquity (philosophy, old religious systems, etc.). That's a much simpler and more grounded explanation for the mayhem post-Rome (we can see it played out in modern history with the mayhem in Germany that led to the rise of Nazism after WWI).
Finally, the last point is well grounded. While we do have evidence of a continuation of pagan traditions well into today, there is a LOT that we don't know about those traditions. For instance, this time of year we celebrate Christmas -a holiday that is supposed to represent the birth of the central figure of Christianity. Yet, this holiday is full of pagan traditions that many practice but have no clue about: decorating a tree, giving presents, making a feast, etc. We take these things for granted but each of these things has at its foundation a pagan practice that predates Christian tradition. We can look at other practices as well within the Church. Ironically, the Jews often consider Christianity to be an idolatrous religion for many of these practices and other things!
I'd argue that work and entertainment arose within human socio-cultural environments for very specific reasons.
Work: This is a very generic and vague term. First, do we consider hunting and agriculture work? These two tasks are a means to provide sustenance necessary for survival. We have to do either of these two things to survive. Would this be considered work? Providing customer service, on the other hand, isn't really something we need to survive. We don't need to sit at a desk or stand behind a counter to really survive. In some facets this behavior is counter-productive to our physical needs (i.e. promotion of a sedentary lifestyle). Is this considered work?
Historically, we see that work arose as a means to keep civilization moving. With advances in agriculture and hunting technologies, vast numbers of people had nothing to do. As idyllic as this sounds -being able to do nothing all day long- it was deemed counterproductive by our overall society. The resultant fix was to set up institutions such as pottery, woodworking, civil engineering, etc. Thus, one could argue that this gave rise to the birth of civilization itself. With all these new trades it became important to develop infrastructure to oversee the functioning of society. In time, this resulted in the need to provide workers with recreation. After all, people have to have something to placate the fact they can't just do anything all day long!
Ironically, I don't buy that narrative. As I mentioned in my prior post, music production has been around a LOT longer than civilization itself. Thus, to make the argument that music and entertainment stem from the need to drown out the abyss of working doesn't make a whole lot of sense. I do agree that there is a definite connection in the development of music from being akin to a linguistic form of communication to art. But then, we can also get into the subjectivity of artistic definition itself, right?