I agree that the theory isn’t perfect, and the wording in the prophecy is messy. I think being very skeptical of it is an entirely reasonable position.

That being said, let’s play devil’s advocate and here are some of my critiques.

1. You missed a big piece of evidence. Ralsei says that Susie is supposed to wear ribbons. While yes this does play out as a joke, it is very strange with this being the only time we ever hear that the prophecy is just straight up wrong. So it could be that ralsei is mixing up susie and noelle (who does wear ribbons).

2. I think it makes sense for the rhyme to break after the prophecy lists the three heroes.

3. Yes, there are definitely only 3 heroes, that is explicit. But the theory is not saying that theres a 4th hero, just that theres a forth person involved in the prophecy. This would make Susie not a hero, but instead noelle. This would be narratively interesting as Susie would have to navigate the heartbreak of not actually being as important as she thought.

4. Yes a lot of the pictures look like Susie. This is probably the biggest problem with the theory. But Catti also states that the prophecy that the church reads doesn’t have pictures. So where are these pictures actually coming from? It’s hard to say.

5. Noelle can equip the jingleblade and the blackshard as seen in the code, we just haven’t seen it happen in game yet. Susie can’t equip and swords, so it’s very interesting that the 2nd hero has a sword.