Expressions and poses don't all have to be the most exaggerated they can possibly be, all the time, frame to frame. That would actually hurt your storytelling. What you want to aim for is the clearest, simplest expression or pose that tells the clearest, simplest version of the story you want to tell. If you're telling an over-the-top action story, it helps to lean into over the top expressions to help convey your idea, but if you're telling a quiet noire thriller, your palette of expressions could be more subtle, to match the mood of your story. It's all about efficient communication. If your over-the-top action character is throwing a punch that could topple a building, it can help to visually amp up the exaggeration to otherworldly proportions, but it's not necessary. That intensely strong character could be the size of Mighty Mouse, and throw a small punch that topples the same building. Contrast creates interest. If every panel is a wildly exaggerated expression throughout the story, you're not creating any dynamics with your characters. It's like hearing a car alarm vs. a piece of music. A car alarm is LOUD, explosive, intense, monotonous, annoying, unyielding, repetitive, boring! But when you listen to a great piece of music there are dynamics that change from beat to beat, creating interest and flow. If all of your expressions are like a car horn blaring, you're going to wear out your viewers really fast. You want to create a rhythm even with your use of expressions to help tell your story. Highs, and lows, explosions, and whispers, and everything in between. When exaggerating a pose or an expression, you don't always have to exaggerate so far as to break it. The advice to exaggerate only means to push your drawing past what you see in your references, because even an intense, dynamic pose can still feel stiff if drawn exactly as it appears in the reference. Push it/exaggerate to tell the story you want to tell. Take a look at comic artist Terry Moore, he's known for his incredibly subtle, and realistic range of expressions in his work, especially his series Strangers In Paradise. He doesn't tell explosive, caped superhero stories, but more real world, slice of life stuff, but his expressions show a full palette of masterful control when it comes to showing the internal monologue of his characters through expressions. Hope this helps.