Yes, of course she’s the main character, but the writing staff claims Chat Noir is Ladybug’s irreplaceable partner while showing Ladybug replacing him on an almost weekly basis. Furthermore, it’s possible to write a partnership of equals where one character is clearly the protagonist.
Maka Albarn is pretty clearly the main character of Soul Eater. She’s an elite fighter, has a special anti-demon soul, has a rare soul that gives her the power to fly, is extremely smart and capable in combat, and brave enough to look the god of fear in the face and laugh (literally). It’s her fighting skills that ultimately carry the day; her partner is literally a tool for her to use to cut monsters apart with. The story is driven by Maka’s actions with the rest of the cast ultimately supporting her.
And yet her partner Soul is still treated as an essential partner and part of the equation. His soul resonance amplifies Maka’s abilities. His calm, cool-headed personality tempers Maka’s driven, occasionally hot-headed personality. He comes up with clever solutions and advises his partner in battle planning and play-by-play strategy. The pair of them together drive out an infection of insanity-inducing Demon Blood. He cares for his partner, pushes her to repair her relationship with her father, helps her come up with strategies outside of battle, and supports her in a way that the story really values…even though he’s not the main character.
When he puts himself in harms way to protect his partner, it is always shown with some kind of weight. The first time Soul gets hurt for Maka is a massive moment in their partnership that has implications that impact the rest of the story and leads to greater trust between them. It becomes a moment where they both resolve to protect one another and become stronger for their partners’ sake
Compare this to the instances where Chat Noir throws himself in front of attacks for Ladybug and the story…doesn’t really do anything with it. It doesn’t really go anywhere or lead to any kind of deeper trust between them; it’s just something that happens on an almost weekly basis at this point. Chat either gets rendered unconscious, taken out of the fight, or otherwise rendered useless and we’re supposed to believe he’s an equal part of this relationship?
Soul is never shown to be superfluous in the ways that Chat Noir is. Especially in Style Queen which shows that Cataclysm isn’t even a unique trait that only Chat Noir can do. Ladybug constantly replaces him with other teammates, defeats akuma on her own, and generally is shown to only need Chat to absorb damage for her. On the other hand Soul is consistently shown (not told; shown!) to be a key member of his and Maka’s team, contributing equally from his own skillset without diminishing the fact that Maka is still the main character.
Tl;DR: You can write an equal partnership even if one character is clearly the protagonist by demonstrating the deuteragonist’s worth (Also SoMa>Ladynoir don’t @ me I’m right)
Woody… he’s been my pal as long as I can remember. He’s brave, like a cowboy should be, and kind and smart. But the thing that makes Woody special is that he’ll never give up on you. Ever. He’ll be there for you, no matter what.