Worse than obsidian if you try and use it like obsidian, sure. But better than obsidian at being a Notion replacement for certain tasks.
Same reason there’s dozens of closed-source note-taking and project management apps. Some have different feature sets and workflows that enable different functionality. One might be great for your specific use-case, another might not. That doesn’t mean the latter doesn’t have any merit, or that it won’t be the perfect solution for someone else who has different needs.