Products like Formspree, Netlify Forms, and Web3Forms try to solve the same general problem as Submit JSON, and they do to an extent, but they leave something to be desired on the UX and DX fronts.
A markup only approach is the aformentioned tools' biggest strength, and it's also their biggest weakness.
The main issue is that they depend on the html <form> element which inherently has bad UX, with default behavior that refreshes the browser upon submission.
The form element is also used for configuration, which feels beyond wrong.
To regain control of the UX we prevent the default form submission behaviour with event.preventDefault().
But now the once simple alternatives have transformed into a spaghetti stitched solution that has you jumping through hoops to submit your data.
See for yourself how obtuse these solutions are: here's how Web3Forms, Formspree, and Netlify want you to submit form data.