gh is great for PRs and issues, but it doesn't know anything about Jira. Here's where the two overlap and where they don't.
I use gh a lot, honestly it's one of my favorite CLIs. Creating PRs from the terminal, checking CI status, reviewing diffs — it's all quick and it works well. So people sometimes ask me why I'd bother with Jitly if gh already exists.
The thing is, gh doesn't touch Jira at all. It doesn't know your ticket is ABC-123, it doesn't know your team's branch naming rule, and it definitely isn't moving your Jira card to Done when you push. Those are two completely different problems.
Not much really. gh is built around GitHub's PR/issue model. Jitly is built around the "I have a Jira ticket, now what" workflow. If your team uses GitHub Issues instead of Jira, honestly gh probably covers you fine and you don't need Jitly at all.