You're right! You can do either.

FormData:

• Works without JS as browsers natively support form submissions without js. Hense why form submissions here are server side.
• Handle file uploads natively (pretty sure)
• Better nexjs integration. Prefetching / loading / etc. (but this isn't really good argument)
• Lighter bundle. i.e doesn't need client side validation libs like zod.

RHF + Zod:

• End to end type safety.
• Better dev experience-- No need for manual formData parsing in example.
• Rich Validation-- Meaning you can better validate client to server side with detailed error messages.
• Better Form State Management especially for large projects.

I often end up using rhf + zod for medium+ sized projects as in terms of long terms dev experience it's much more efficient for me.

For any small projects to get things done, I use next's native form.