> You can write one last Jenkinsfile that runs Dagger

I'm very confused by this sentiment. This approach loses the best of existing CI tooling does it not?

Jenkins users lose understanding of what's actually being executed, what stage they're in, and how long it took. It might provide convenience, and the a (great) benefit of running locally the same as in your CI environment, but it seems to me this would make it difficult for devs to easily understand where/why their build failed, since it just has one megastep.