Workflow is mainly for simple orchestration with few integrations. You need to write code (in YAML or JSON).

App. integration is best when you are implementing a business workflow with integration with third-party solutions through connectors.

You are right, Application Integration UI is easier to start, and no need to be tech to start using it.

You have this interesting article:

https://cloud.google.com/workflows/docs/choose-app-integ-or-workflows#:~:text=If%20you're%20integrating%20business,infrastructure%20automation%2C%20consider%20using%20Workflows.