This is not true for stability in practice: the action often depends on a specific Node version (which may not be supported by the runner at some point) and/or a versioned API that becomes unsupported. I've had better luck with @main.

   uses: actions/checkout@v4

Yet with GHA I need to update actions/checkout@v2 to actions/checkout@vwhatever (or, what I'm doing now, actions/checkout@main because the actual API haven't actually changed) because... some Node version is "out of maintenance"?!

GHA is literally code execution as a service. Why would I care whether the Node runner has a security vulnerability?

Would GitLab have been better? Maybe. But chances are that there is another edge case that is not handled well there. You're in a PaaS world, don't expect the platform to adjust to your workflow; adjust your workflow to the platform.

You could of course choose to "step down" (PaaS to IaaS) by just having a "ci" script in your repo that is called by GA/other CI tooling. That gives you immense flexibility but also you lose specific features (e.g. pipeline display).

I think, however, that starting from the examples might help with good API design: if you design your API to be "core concept first", this will likely lead to an API that _can only be used after you understand the core concepts_, which is not great when people are only occasional users.