While legacy decorators are not part of the spec, they are still practically better than the ES decorators.
I think, we would want to gracefully move to ES decorators once they implement support for the context.
Right now without context, ES decorators are useful for very limited use-cases.
Btw, legacy decorators should never be removed, unless TypeScript wants to blow up the entire ecosystem of TypeORM, NestJS, MikroORM, Inversify and so on.