Would a rewrite necessarily benefit the business? Can you make a strong case for that?
If not, start writing tests, try small incremental refactorings, ask your manager to hire more people, maybe someone not as qualified as you but that can take on some more of the unpleasant activities. Maybe you can negotiate some 20% time? Use that time to build tooling to help you do your job better. Share it with the world. Management won't give you these liberties? Find another job. And ask the next company to show you their code metrics before you seal the deal.
If not, start writing tests, try small incremental refactorings, ask your manager to hire more people, maybe someone not as qualified as you but that can take on some more of the unpleasant activities. Maybe you can negotiate some 20% time? Use that time to build tooling to help you do your job better. Share it with the world. Management won't give you these liberties? Find another job. And ask the next company to show you their code metrics before you seal the deal.