It's cost me hundreds to thousands of dollars to implement nontrivial workflows because of how the YAML is parsed (for example, empty strings when using a secret that has been renamed or removed) and the lack of introspection or debuggability when something goes wrong.
It's gotten to the point where new any new workflows I write are thin wrappers around a single script and I don't import any actions besides actions/checkout (even that has been bug prone, historically).
All that said, it's not like other platforms are better. But they certainly are cheaper and don't have dumb breakages when you need cross platform builds (has upload-artifact been fixed for executables on MacOS yet?)
Not being able to execute it locally has also wasted a lot of time, and people needing to make 50+ changes to the master branch until they get it right.
Why can't I have a separate interface where I just say "build this Github project, and put the content on this on-prem server/kube cluster/VM/whatever."
Another trick that works well is putting GitHub Actions in an entirely separate repository. There's nothing to stop actions in one repo from checking out code from another - I use that trick quite frequently.
You do have to jump through a few extra hoops to set it up so that code in your actions repo starts running automatically on commits to your main repo, but you can do that with a small action in the main repo that triggers a build in the actions repo.