It's an issue tracker, with some project management/agile bolted on

Notion databases easily allow dependencies, integrated relationship tracking and multiple ways to visualize a project roadmap. Can't speak to JIRA but Notion is continuously releasing new updates that respond to user needs. There is a major downside to this of course. As a solopreneur I find it frustrating that Notion's updates tend to serve corporate needs, but it's a good business strategy and allows Notion to continue to serve others with its free version.