I have the exact opposite experience. GitHub CI is probably the worst CI I've used so far (except for custom homegrown messes), and Gitlab CI by far the best.
GitLab CI isn't even on the radar. I'd take Actions or Buildkite anyday over the existing offerings. I'd argue the GitLab CI ecosystem is non-existent.
When I talk to Hashicorp or AWS they provide tooling specifically for GitHub Actions. I don't see the same level of vendor commitment when it comes to GitLab. If I'm not going to get vendor commitment I might as well run buildkite which is awesome or even look to something like Tekton for Kubernetes if I'm just doing Kubernetes anyways.