>you just use naive two-way binding with an actual decimal value this means you'll get in the way of the user trying to manually enter a decimal value

Naive one way binding is useless as well.

>two-way binding of the actual form fields becomes an implementation detail.

Kinda. In fact in Vue two-binding is a syntax sugar for one way binding and on change events.

The difference between them, is one requires less lines of code and is less powerful.

If you do need react-style form input, then you can do it that way.