Seems to me that one-stop shop is very different from one-stop tool. GitLab is aiming for the latter, whereas Atlassian (at least when I was using those tools) seems much less integrated.

Jira may be the most comprehensive issue tracker (which isn't necessarily attractive -- but then they have Trello now, too), but on the version control and CI front I don't think Atlassian will have an easy time competing against Azure/GitHub/GitLab.