How do I get better at complex motion graphics?

You have crossed a real line. The basics work in your hands now, and that took time and patience most people never give a craft. What is left is the hard part, and it feels far away because it is genuinely harder, not because you fell short. Complex animation is not one big leap. It is many small ones stacked together. Pick one thing that stumps you, take a single shot from work you admire, and rebuild it piece by piece until you understand why each frame moves as it does. You learn the difficult by taking it apart, not by staring at the whole. Be patient with the gap between what you can picture and what you can make. That gap is where every skilled person has stood. It closes slowly, through reps, not through waiting to feel ready. Do one hard piece this week, badly if you must. The mastery you want is built from exactly these attempts.