Constantine's rule was known for its success. For a brief period, Rome's decline was halted and military and social victories were abundant. The imminent collapse of the Roman Empire was halted.
I anticipate that the effects of religious subversion would take a considerable amount of time to manifest. The objective isn't merely to alter people's political ideologies but to shift their fundamental worldview. The transformation of metaphysical concepts, influencing ideology and subsequently politics, is a gradual process.
Notions such as original sin and the idea that the less fortunate are less sinful than the prosperous will bring about societal changes at a slow pace. The transition from glorifying strength and the power to dominate to celebrating meekness and the willingness to serve seems, to me, detrimental for the existing Roman empire.
The upheaval is profound, with fundamental perspectives undergoing a complete reversal. The shift from perceiving nature as beautiful and true to regarding it as sinful and deceptive is one such example.
Under Christian norms, the admirable qualities in a leader no longer revolve around justice, strength, wisdom, civic virtue and nationalism. Instead, leaders are esteemed for their devotion to the faith, adherence to the Christian ethical principles, defense and propagation of Christendom, acts of charity like supporting the impoverished and tolerance like showing compassion to foreigners, and the demonstration of pious conduct. The magnitude of these transformative shifts suggests that their impact cannot be minor; in fact, it would be nothing short of miraculous if they did not significantly alter the societal fabric and the destiny of the Empire.
Tl;dr: Changing the metaphysics of the Roman people does not immediately alter anything else. Slowly and over time, the people will adapt their societal systems to align with their metaphysical beliefs.
If Jews hated Christianity
The central tenet of Judaism emphasizes the prohibition of idol worship, making it crucial to exclusively worship the god of the Israelites. Any deviation from this principle is seen as blasphemy, creating a lasting dislike for Christianity by Jews.
As per Torah Judaism, it is permissible for a Jew to pray in a mosque, as Islam doesn't involve idol worship. However, the veneration of Jesus, the Trinity, or Mother Mary prohibits a Jew from praying in a church.
Maimonides, a highly influential rabbi who disliked both Christianity and Islam, asserted that both religions play a crucial role in god's plan to disseminate the Torah globally and prepare people for messianic acceptance.
This view by Maimonides is the reason you have people like Ben Shapiro and Denis Prager working hard to make the US more Christian.
The prevailing perspective among Rabbis regarding Christianity is that it is Idol worship, yet it is considered preferable to Paganism. This assessment arises from historical circumstances, as under various Pagan rulers, practicing their religion was often prohibited for Jews.
Under Christianity and Islam Jews observing their religion was generally permitted.
Tl;dr: Jews did not like Christian Rome but most definitely preferred it over pagan Rome.
why would they infect them with an Emperor who is mostly remembered for his success and got the "the Great" epithet and is generally well-regarded even to the current day?
Paul authored a revolutionary book, yet he did not possess the authority to choose the Emperor.
It is likely that both Paul and Rabbi Gamaliel anticipated Christianity causing more immediate turmoil in Rome, providing an opportunity for Jews to reclaim Jerusalem before their diaspora settled into new lives. From their perspective, assimilation was a concern, and they might have hoped for a quicker upheaval.
This assumption is grounded in the early Christians' expectation of an imminent apocalypse. However, the reality turned out to be a gradual process, requiring subsequent Rabbis to adapt to the unfolding circumstances.
Despite potential concerns, Jews were not in an unfavorable position within Christian nations. Christianity facilitated money lending for them, a practice explicitly commanded by the Old Testament, while Christians were prohibited from such activities.
Deuteronomy 15:6
"For the Lord your God will bless you as he has promised, and you will lend to many nations but will borrow from none. You will rule over many nations but none will rule over you."
Christianity, as an ideology, is not inherently negative. In fact, at its outset and superficially, it embodies many positive aspects, such as aiding the impoverished and infirm and promoting love for one's neighbor and seeing everyone as equal under god.
I would expect early Christian leaders like Constantine to be very popular. His religious freedom doctrine was also well received among Jews.
However, the ultimate consequence of principles like "love your neighbor" and the equality of all humans under God is the gradual erosion of Roman nationalism. Initiatives such as assisting the sick and the poor, establishing welfare programs, ultimately result in the expansion of a dependent lower class relying on assistance.
"Das Gegenteil von gut is gut gemeint." (The opposite of good is well-intentioned.) -Henrik von Holtum
Expressing absolute certainty is challenging, but several actions undertaken by Christianity in today's world, such as advocating for immigration and opposing nationalism and ethnic cohesion, would certainly have occurred in ancient Roman times. After all, the foundational text has remained relatively unchanged, maintaining a universalist perspective and endorsing the vision of a global government of all people under Jesus Christ.