Fuck Katherine, all my homies simp for Rosa instead.
I wish Musa had been an Ethiopian Christian, it would have been far more interesting narratively.
Picture this, Musa as a soldier fighting for Ethiopia against the Mamlukes and Ottomans, just like the European kingdoms are. He gets captured in a battle, but as a nobleman he is sent to the capital as a captive. He manages to break out during the chaos of war or a siege or whatever, and makes his way west into Europe to continue the fight in any way he can.
This does three things. One, it does a decent job of explaining why he's with Sigismund. Sigismund as the King of Hungary has a vested interest in curtailing the spread of Islam since the Ottomans are practically in his back yard. Their interests line up, easy team up to kick Muslim ass. Two, it makes Musa mirror Henry quite a bit. His home is invaded, he swears revenge, he joins up with an army, where did I hear this one before? It would make their friendship a lot more believable Three, if it would really help the sappy "we are all same" messaging by you know, actually making Musa similar to the Bohemian.
It still would definitely have pissed people off, but it would have been cooler. Plus he could have dropped truth nukes on us by explaining the Arabic slave trade and how they kidnapped Christians to be slave soldiers and castrated their slaves.