This is exactly what we want though. We don't need the new fancy shit on a regular cadence. Issues, Code, PRs and 1 line checkbuild scripts are all we care about. Everything else is built into our software.
What is really rough about GHE is that you can't choose a lot of the features or IMO baseline requirements like caching that you've probably come to expect from github.com, and may have been around for years. At least not until they can get GHE to parity with .com.
At the very least, they use just absolutely incompatible yaml files for their CI pipelines (in, of course, an incompatible location in the repo)
But probably the bigger obstacle would be their incompatible API (and incompatible auth to it); that means one cannot grab a cool "github bot/tool for doing $X" and expect it to do anything reasonable in GitLab
Based on my contact with GitLab's built-in other scanning tools, I wouldn't trust their vuln management further than I could throw it, so you're likely not missing much on that front