I think it would be annoying too with many form definition in controller, especially the apps will involved many form.
But Play!Framework make developer to write code more flexible. You can mix plain HTML inside scala template helper like this :
@helper.form(action = routes.Application.submit) {
<input type="text" name="username">
<input type="password" name="password">
....
}
In my opinion, the scala helper actually helpful with form to update data that have been created before. Because it will bind the existing value into the default input value. And additionally, it also help to display error that caused by object validation.
If the form is not considered the previous value, like login form, I think the use of plain HTML input will be considered better.