With GitLab, the convenience is just another option, though in my experience it's a very powerful option that will get you further, easier, than many of the alternatives. There's nobody saying you can't run your CI on Jenkins or Travis, or deploy to whatever, wherever. GitLab gives you some powerful options built-in, whereas GitHub _requires_ you to bring your own for many of those use cases.

Not to mention it's open source, so if you find something you need, you can actually contribute it to GitLab. Not that it won't be work for you, but it's an option beyond asking somebody to put it on their dev team's roadmap.