If it's a simple site, everything can be done manually. If it's a complex site, I wouldn't risk to mess things up with migrations. I haven't tried JConverter myself, but I know it has limitations and hasn't been updated for a few years. You can just try and see yourself, it might work.
Joomla is a dying product. The benefits of WP and a plethora of plugins, templates and technical help out there is such an advantage over Joomla. Joomla likes to create new versions that do not transfer vs WP that just keeps updating their system. I would bet that any tool used to move data from WP to Joomla will work like junk and create more work for you than if you started fresh and built your site with Joomla.