In particular, the backstories of most of the other witches are barely even touched upon, and all the more disappointingly, the telegraphed obvious "crisis of conscience" moment in Maria's character development was barely mentioned and breezed right past before you could even blink - that is, there's one particular battle where France is going to ambush the retreating English army and wipe them out, thus forcing the English to sue for peace, ending the war.
However, because Maria meddles in every battle (including this one), the English are able to rally and counterattack, causing more bloodshed and prolonging the war interminably. Because Maria couldn't stand to let even one single battle play out without her interference, she was directly responsible for countless more deaths. But this is only mentioned in passing, and a great opportunity for Maria to experience inner turmoil and character growth falls straight to the wayside.
As a result, Maria experiences almost no character growth at all, and neither does her love interest Joseph - they are pretty much the same people at the end of the story that they were at the beginning. Maria is supposed to be a parable on conviction and principle, but her lack of inner conflict and being completely devoid of any self doubt in the face of the consequences of her actions make her seem just as blinkered and unthinking as Michael - just as much a slave to her childish wants as he is to Yaweh.
Much more interesting are the supporting characters -
Garfa the mercenary turns from roguish antihero to morally rudderless antagonist, willing to murder to advance himself and commit rape as a "job." He breaks bad in a big way, and almost becomes a true villain.
Ezekiel the angel develops free will, and as a result, is trans-substantiated to human form since she is no longer fit to be of the Heavenly Host.
Viv and Edwina the witches both experience learning and growth, the former coming around to respect Maria's militant pacifism and the latter finding her courage to do what's right despite her crushing fear of persecution.
And probably the most interesting character of them all is Bernard the monk, a cunning but devout man of the cloth who, through his interactions with Maria, has an epiphany that mankind doesn't need God anymore. Which is kind of a dangerous thing to espouse in 15th century France.
The main characters aren't the only ones to not get any growth, though - Archangel Michael is unchanged from the start to the finish, but it's by design and less irritating - Michael represents the danger of absolute faith completely stripping you of self determination. Michael literally has no mind of his own, makes no decisions, has no judgement. He is merely God's direct representative on the mortal plane, and his robotic voice, appearance, and mannerisms underscore this fact. Michael is not a person, he is an instrument, a tool - and it was Ezekiel's evolution into thinking for herself that led to her being cast out by God because God doesn't want his tools to be thinking for themselves.
But the cherry on top of all the squandered potential is the ending, which is probably as close to a literal Deus Ex Machina as anyone has ever seen outside of a Greek play. The final dispensation of Maria and Ezekiel is confusing in its self-contradictions. In one moment Michael is literally telling the world that God has decided to accept Maria as a "neighbor" and will no longer persecute her, and then the very next moment he's directly setting in motion the inexorable process of stripping her of her magic power. If that was the plan all along, if he's just going to make her an ordinary human, why bother broadcasting to the world that God would accept her existence as a witch? And her power is gone just like that, without any real romantic payoff? Maria and Joseph don't even get a "big kiss" at the end when they become a couple. It's just "Ta-da! The end!" and then a literal "happily ever after" mini-narration. It feels like the sort of thing a series does when it is suddenly cancelled.
But, despite all that, it is an anime with its moments, and I've sat through much, much worse. It's just a shame because it could have been really epic. It could have had some FMA level whams and philosophical conflicts/quandaries. But it only brushes past them or hand-waves them away. Too bad.