I have been having a play with the new 2.5 Form Builder and it still strikes me as odd that you can’t easily place the Submit button in the layout. It still lives in the “Form Footer” element which is adjacent to the Form Body element in the DOM. This means that you are limited in how you can customise the overall layout of the form.
I think the form builder is a good step forward, but advanced users should be able to control the markup of the form more directly using a code editor or a proper layout builder with section/row elements, column elements etc. (not dissimilar to how the popular page builders work). Alternatively, it could be as simple as allowing for an “advanced” mode with the HTML element which when Checked doesn’t output the gfield wrapper markup, and instead just outputs the contents of the field. This way, you could use the fields to create wrappers for sections of the form by specifying “Open” and “Close” tags for sections, divs etc.
I know that may mess with the “CSS Grid” that has been adopted for the forms in 2.5, but just a suggestion.
I have lost count of the number of times I have had to “hack” a layout solution using floats, negative margins and a bunch of media queries 