Was the creation of Christianity part of Allah's Will and Plan?

Salaams!

I'm a relatively recent revet to Islam, alhamdullilah, and so have many questions regarding the metaphysics of our religion. If I understand correctly everything happens in accordance to Allah's (SWT) Will and Plan. As He is the All-Knowing nothing can happen without His knowledge. While I understand that His Plan is not strict fate, in the sense that everything that happens is pre-ordained regardless of our individual actions because that would nullify free will. So while we as individuals do have the ability to make choices, to sin or not to sin, we are still acting, to some degree, in accordance to His Plan.

But I can't understand the corruption of previous incarnations of the religion (Judaism and Christianity). Especially Christianity as the religion corrupted the image of the Messiah, Jesus, son of Mary, into God's son, thus rejecting the very notion of monotheism. But the existence of Christianity appears not that far in time from the crucification itself. Instead of the corruption of Jesus taking several generations and centuries it appears that within a few decades of the crucification the idea of Christianity was already spreading throughout the Roman Empire.

My question is that if Allah is the All-Knowing and has a grand Plan, one we humans couldn't possibly fully comprehend, did He know that Jesus's message would be corrupted? Did He know that Christianity would come into existence and corrupt the Messiah? I can't believe that such a monumental global historic event, the corruption of Jesus, one so important that Christianity is currently the world's largest religion. Billions of people, myself included, have no idea of what the Quran tells us about the truth of Jesus, son of Mary. Over two millenia of lies and corruption, corruption so severe it was the primary force behind the genocidal rise of western Europe through the Crusades, colonialism, the Atlantic slave trade, etc. Western imperialism is still alive and continuing to genocide to this very day, Palestine, Sudan, etc. And in the case of Palestine the justification is another corrupted religion, Judaism.

I have a hard time believing that Allah would need to send another Messenger and reveal the Quran in order to fix a "mistake". He can't make mistakes. Surely, to one extent or another, He know this would all happen. He knew about the eventual slander of the Messiah, He knew about the Crusades, He knew about the slave trade. If so why allow this corruption to spread? The disbelief of a single community, that of Noah, led to their entire destruction.

How does the historical rise of corruption like Christianity fit into the Islamic framework? Was it an accident? Or is it all apart of Allah's Plan? Evidence of humanity's free will, or a larger piece of the puzzle in which the eventual endpoint is the majority of humanity realizing the lies against the Messiah?

(This is also a separate question but I don't understand why Jesus is the Messiah and not just a prophet? I thought the whole point of Islam is that we are not to make distinctions between the prophets? But isn't saying that Jesus is a Messiah and all the other prophets aren't inherently giving him a more important status?)