Yes, this is all true. However, this approach has more downsides than just nil and cumbersome syntax imo. It takes more memory and pointer-chasing than "proper"

Yes, this is all true. However, this approach has more downsides than just nil and cumbersome syntax imo. It takes more memory and pointer-chasing than "proper" sum types would require, and while you can "seal" the type, there's no exhaustiveness checking.