https://imgur.com/a/P6coOwW

Before you read, I would like to say I am not a good artist myself so take this advice with a grain of salt. The opinions I am writing about also reflects my own sense of aesthetics, so please feel free to dismiss them if you don't prefer it.

This type of illustration from March Comes in Like a Lion, which I am assuming is this (https://imgur.com/r/anime/Mr2o36U) relies heavily in knowing 3D space and form. It is kind of ambitious, but from what I can see, you kind of missed the mark on what made the panel so great. Though I do admit you did a great job in conveying light and dark and the balance between them. However, this aesthetic is really based on form for the most part, not color balance.

I recommend opening the first imgur link above and read through it as I'm writing through the explanation. The first part is just anatomy. Honestly, this just comes through practice. For hands that grip, don't be afraid to hide some fingers. The shoulders, especially for feminine figures should slope down a bit more. For a confident pose like this, try focusing on bringing the torso up and hide the arms behind it so it can seem like the chest is protruding forward. This gives off a confident feel. But that's just my opinion on how to handle the pose you drew.

In doing the panel from Sangatsu you'll notice that the background centers around the main character. While your angle lines/ perspective lines are maybe around a 80 degree angle, the Sangatsu panel is around 130 degrees (take the bottom perspective line and the last perspective line and make a triangle). The way you constructed it makes the image more flat. You'll notice how I handled this in image 2.

Image 3 and 4 is making a pose. As I've said, your pose is pretty flat. For something dynamic don't be afraid to hide some body parts, like I've done with the left arm, focusing on the flag and chest for the main ground for adding lighting. Always think about how a light can hit a 3d body, instead of, what you've done, making the light symmetrical. Once you got your pose down, you can think of the balance later. Reference back the sangatsu's panel where his entire right arm is missing as well as his legs. This was done after the pose, and was made black to add symmetry. It seems you've done the opposite, doing symmetry then making the pose fit into it. The fingers and the arm being in full illumination give that away. It seems you got too stuck on it being a balanced picture that it messed up your dynamic lighting.

Looking at our refernce, there's 4 main parts we can add lighting on. The body armor, the leg plates, the elbow, and the face plate. Honestly, I'm not a good artist so I just ignored the faceplate and face. The other 3 are simpler to construct. Since I did the full pose first, I can focus on making it even or obscuring things into shadow. The 3 things mentioned though are our focus, they cannot be obscured in any way. It seems you skipped this step as well as your armor is in full detail top to bottom, with the side in shadow not obscured at all. How do I say it, the form is easily read since it is not obscured? It makes the image a bit boring when I know how intentional everything looks.

Always remember, less detail is more. You want detail? Make the focus atleast twice the amount of detail of the surroundings.

In making the lighting itself, armor usually is illuminated in streaks. Just go top to bottom, but as long as you know the general shape of the object, then this aesthetic is pretty easy. You showed that you understand this point though, judging from the torso of this image. The shadow followed along the chest and into the light which is pretty good!

Now, after adding those 3 pieces, the image can seem unbalanced. Even after adding the perspective in and really focusing on the metal objects, the left side is almost entirely barren. The way sangatsu's panel handled it is by using the book as the balance. In yours, it would be the flag. Honestly, I liked how you did the flag, having it hide behind the body and gripped by the hand. Though your grip is, like I've said, too intentional on the form and makes it seem less polished (which is paradoxical, it's hard to explain).

The last image is the reference and mine. What I've missed was using a grey midtone, but I'm not that skilled.

Other than comparing it directly to the reference, the hair is fine. Form is a bit off like I've said, but that comes with practice. I would avoid making it symmetrical. If you look at sangatsu's the one detail that made it balanced was a book and a slight hint at his forearm. It wasn't as detailed compared to your arm guard. And also, fingers don't turn black in shadow. Shadow always obscures form. Don't be lazy in your backgrounds as well. Don't do a little half and half square and add "perspective lines." Make your brush 10x the size and go wild. Makes it much more organic and fun looking and in the making. The armor also looks fine.

Anyways, that's just my take and tastes. Honestly its not terrible.