I wrote another post on some of the factors that contributed to the rise of Christianity before the time of Constantine that may interest you here.

I haven't watched the Youtube Video or done any research on the professor. However, I would caution against generalizing the thought that polytheistic religions are more tolerant than monotheistic religions. This is not necessarily the case historically. Even if we narrow it down to the Mediterranian, we see that the polytheistic Greeks did not tolerate Socrates, who was charged with not acknowledging the city's gods. In Rome there was the suppression of the Bacchanalia cult in 186 BC, the Roman authorities themselves, or the victims' families, executed about 6000 members of Bacchic groups. (Bremmer, 17). Of course, these events happened almost four and two centuries, respectively, before Christianity arrived on the scene. Still, they serve to illustrate that just because a society is polytheistic doesn't mean they are tolerant as we understand the word today.

Documentation of Christian violence against pagans that are literary in nature, such as Life of Porphyry by Mark the Deacon, which describes how bishop Porphyry ended the worship of Marnas, the chief god of Gaza in Palestine, have recently come under question for their historical accuracy (Bremmer, 23). Bremmer also notes that in the past few decades, archeologists now believe that there were fewer instances of destruction of temples by Christians in Eqypt than previously thought (26). On the opposite side of the coin, there is also research that says that it is difficult to get an accurate number of Christians that were martyred and that Christian sources likely exaggerated the number for a variety of reasons.

Your question, however, is about the relationship between pagans and Christians before the persecution of Diocletian.

Unfortunately, as is often the case, history is written by the victors, and the opposing voice difficult, if not impossible, to find. Since Christianity "won," there is not much historical documentation that opposes it, and what we do have is snippets Christian apologists used. From a historical standpoint, these are somewhat unreliable and are difficult to apply to reconstruct what opponents of Christianity may have genuinely been thinking. The writings we do have to draw conclusions from that are not written or edited by Christians are understandably from the educated class.

No one can pinpoint what began the persecutions of Christians by Decius in 258 or Diocletian in 303 C.E. Some historians believe that a natural disaster like famine, or wanting to secure victory against enemies meant that emperors wanted to ensure the blessing of the traditional gods. That is to say, it not so much that these emperors woke up and said, "I am going to persecute Christians," but that they wanted to bring back Roman tradition, which seemed like a way that had always worked before and the Christians had to make their decisions accordingly.

One source for pagan attitudes towards Christians is Lucian's description of a Christian group in Palestine in his Death of Peregrinus. This writing is a satire and needs to be treated and read as such, but it does tell us what Lucian and his audience may have assumed about Christians. According to scholar John North, the critical thread in this narrative is that the overarching view is that Christians are the victim of a con. It was considered odd at the time, that Christians did not seem to have a fear of death and that many were willing to be martyred. It is not farfetched to think that some would have thought of Christians as victims who had been duped.

On the other hand, some intellectuals did seem to attack the exclusiveness of Christianity referenced in your original post. Hierocles used The Life of Apollonius of Tyana to attack Christian claims to superiority. (Praet, 54) Interestingly Christian belief that worshiping other gods was idol worship and responsible for the degradation of Roman society was a belief they shared with the philosophers of the time. The latter also criticized religious practices they felt led to the social ills of the time (Clark, 36).

I hope this and my other thread answers your questions.

Sources:

Bremmer, Jan N. "Religious Violence between Greeks, Romans, Christians and Jews". In Religious Violence between Greeks, Romans, Christians and Jews, (Leiden, The Netherlands: Brill, 2014)doi: https://doi-org.dtl.idm.oclc.org/10.1163/9789004274907_003

Clark, Gillian. 2004. Christianity and Roman Society. Key Themes in Ancient History. Cambridge: Cambridge University Press. doi:10.1017/CBO9780511803536.

North, John A. 2017. "Pagan Attitudes." Chapter. In Christianity in the Second Century: Themes and Developments, edited by James Carleton Paget and Judith Lieu, 265–80. Cambridge: Cambridge University Press. doi:10.1017/9781316691601.017.

Praet, Danny. "Violence against Christians and Violence by Christians in the First Three Centuries: Direct Violence, Cultural Violence and the Debate about Christian Exclusiveness". In Religious Violence between Greeks, Romans, Christians and Jews, (Leiden, The Netherlands: Brill, 2014)doi: https://doi-org.dtl.idm.oclc.org/10.1163/9789004274907_004