Agree with this 100%. And this will be especially important if we get control over how the buttons are to appear when the form is published, as I posted here.
@RussellGove as a workaround you can add a custom data card and then add a button to it, and then OnSelect on the button to "SubmitForm(SharePointForm1)". That works from preview mode. You just have to remember to hide/delete the data card before you publish.