Why am I still treated like a stopgap when I can do the work?

You know what you can do. You've worked the differential, caught what others missed, carried the judgment call when it mattered. Then someone with a different title gets the credit, or the pay, or the final say. This is not in your head. It is a real gap between your ability and your position. Here is what will not close that gap: waiting for the system to notice, or letting the anger sit and harden into bitterness. Neither moves you one inch closer to where you belong. The system is slow not because it is cruel, but because roles were built before people like you existed in this form. That is not an excuse for it. It is just the truth about why shouting at it does nothing. What is in your power is smaller than you'd like, but it is solid: what you document, who you ask, what you ask for, and how long you wait before you decide to leave. Start with those. Stop spending yourself on anything else.