Correct, you can create requirements anywhere, I just feel requirements are more important, and long-lived than a transitory Jira ticket.

E.g. A Jira ticket moves to "Done", the requirement is complete, and people are happy. But the important info on that ticket has essentially disappeared - obviously you can mine your thousands of tickets for historical info - but no one really does.. as it's mixed with bugs, changes, improvements, conversations etc.

I don't know how exactly you'd do that and depending on the project it might be fine.

One important feature of a requirements tool is that it allows you to "tag" a set/document of requirements with a version that corresponds to your released artifacts and create "diffs" between such versions. I don't think that's possible with plain Jira(?)